The Role of Mineral Nutrients in Grapevine Physiology

Dr. Stephen J. Krebs, Viticulture and Winery Technology, papa Valley College

Calcium (Ca)

Magnesium (Mg)

Sulfur (S)

Where Found In Vine

Amino acids, DNA and chlorophyll

ADP/ATP energy transfer in photosynthesis

Osmotic relations in guard cells; temporary cation in biosynthesis pathways

Ca+2 Cell wall component

mg+2 Chlorophyll molecule

sa4 -2 Some amino acids, many biochemical compounds

Sugar transport, pollen tube growth, cell division

Chlorophyll formation, pollen tube growth, internode elongation

Chlorophyll formation, biochemical activator

Nutrient/Symbol

Nitrogen (N)

Phosphorus (P)

Potassium (K) (Latin: Kalium)

Uptake Form

NO3 NH4

PO4-3 HPO4-2 H2PO4-

K+

Boron (B)

B03 -3

Zinc (Zn)

Zn+2

Iron (Fe) re+2

Copper (Cu) Cut , Cu+2

Enzyme activator

Nickel (Ni) Ni+2

Component in urease and nitrogen metabolism, especially in legumes

Manganese (Mn) Mn+2

Enzyme activator

Molybdenum (Mo) Mo04 -2

Nitrogen utilization (Pronunciation: Mo-lyb-de-num)

Chlorine (C1) Cl-

Photosynthesis reactions

REVISED: 01/2004

V\

THE RELATIVE EXTENT THAT PLANT NUTRIENTS ARE ASSOCIATED WITH BIOLOGICAL, CHEMICAL AND PHYSICAL SOIL REACTIONS

Nutrient

Chemical

Forms

Cation Anion Precipitates

Found in Mineral Relative Symbol

Used

Adsorption Adsorption as insoluble organic Entrapment Mobility inorganic forms forms

Nitrogen NH4*

high

slight to moderate immobile moderate to high

NO3 - none to slight to slight moderate

moderate to high

Phosphorus

Potassium

Calcium Ca

Magnesium Mg

Sulfur

Zinc Zn

Iron Fe

Nickel Ni

Manganese Mn

Copper Cu

Boron

Molybdenum Mb

Chlorine Cl

H2 PO4

HPO4 -

K+

Ca++

Mg++

SO4 --

Zn"

Fe", Fe+++

Ni"

Mn++

Cu++

H3B03

HMo04 -

Cl -

moderate high slight to moderate

slight to moderate

slight

slight

slight

high

high

high

high

high

moderate

moderate

high

none to slight

mobile

immobile

immobile

immobile

immobile

mobile

immobile

immobile

immobile

immobile

immobile

mobile

immobile

mobile

high

high

high

high

high

high

high

high

slight to moderate

moderate

moderate

moderate

slight to moderate

PETIOLE SAMPLING INSTRUCTIONS

As close to full bloom as possible, take your samples following the easy instructions below:

1. FOR ROUTINE SAMPLING - To determine fertilizer needs; take the petioles which occur opposite either of the two basal flower clusters (see illustration below). Tear off the leaf blade and save only the petiole. Remember, the petiole is the part that connects the leaf blade to the cane.

2. TROUBLE SHOOTING - Sample at the time when symptoms occur. Take the petioles from vines showing abnormal symptoms. Then take petioles from vines that appear normal, from the same general location on the shoots which show abnormalities. Both samples should be taken from the same vineyard, variety, and soil type. We then analyse both normal and abnormal petioles, compare the two, and decide on a course of action. If it is not full bloom time, collect the petioles from the most re-cently developed, full-sized leaf. This is commonly the 5th or 6th leaf from the shoot tip.

3. Sample Size - Sample one vine, then skip a few vines. The main objective here is to obtain a good representation of your vineyard. Sample until you have at least 100 petioles, 150 if you have small vines. Don't mix different varieties or soil types.

4. Sample Handling - Drying your samples yourself is not necessary unless you plan to ship your samples directly to our lab in Ukiah (use UPS). You can dry them by placing samples in oven; turn heat as low as it will go, prop open the door and dry them overnight. If you don't want to worry about all this, just put the samples in paper bags (DON'T USE PLASTIC), fill out your sampling form (enclosed), and drop them off at Vinquiry or The Wine Lab. Indicate on the sampling form if you have ap-plied any foliar nutrient sprays this spring and we will wash them before analysing.

select petiole opposite either one of the basal clusters at full bloom

save petiole - discard blader

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Nitrogen

The nitrogen status of a vineyard can be established by leaf blade analysis. It is important to evaluate total nitrogen (%N) at bloom in blades as weather patterns can cause fluctuations in petiole nitrates some years. Generally, bloomtime leaf nitrogen content above 3.0% appears to indicate an adequate nitrogen content.

3.8%

High

3.3-3.7%

Moderately High

2.7-3.2%

Normal

2.7% or less

Low

Copper

Sodium

Chloride

Petiole phosphorus at bloom is satisfactory between 0.1 — 0.15%.

Petiole potassium concentrations are satisfactory above 1.5%, deficient below 1.0%. Vineyards with low or questionable potassium concentrations should have leaf potassium concentration evaluated at berry softening. Leaf values are normal within 0.6% to 0.8% at bloom.

Generally, zinc concentrations in petioles and leaves satisfactory above 25 ppm.

Maintain petiole and leaf levels above 25 ppm at bloom.

Satisfactory petiole levels are above 1.0% at bloom.

Petiole levels are satisfactory above 0.3% at bloom.

Plant tissue calcium to magnesium ratios in the 1:1 range (Ca:Mg) can indicate adverse soil calcium to magnesium ratios. If magnesium concentrations are approaching, equal to, or greater than calcium concentration in plant tissue; then a soil evaluation is advised.

Boron is satisfactory if petioles and leaves are at above 35 ppm at bloomtime. Research has revealed the existence a temporary boron deficiency in early spring even when vineyard levels increase to normal by bloom. The questionable range for petioles at bloom, under this situation, would be 26-30 ppm. Early season symptoms include faded yellow foliage, burnt clusters, stunted and deformed growth. Boron concentrations in petioles above 100 ppm pose a toxicity hazard. Excessive boron occurs above 1.2% in petioles and 0.8% in leaf blades.

Petiole levels are satisfactory above 8.0 ppm at bloomtime and leaf values above 4.0 ppm.

Bloomtime petiole and leaf sodium concentrations are satisfactory below 0.5%. Harvest blade analysis is suggested in areas with high sodium content at bloom.

Bloomtime petiole and leaf chloride is satisfactory below 0.5%. Harvest blade analysis is suggested in areas with high chloride content at bloom.

Phosphorus

"Potassium

Zinc

Manganese

Calcium

Magnesium

Calcium to Magnesium Ratios

Boron

F:\CLIENT\INTERPRE\COASTAL2 Grape.doc I 1 / 11 /99

Optimizing Vineyard Nitrogen Fertilization Stephen Krebs

Introduction Nitrogen is the fertilizer element most likely to be deficient in

vineyards. It is also the fertilizer element most commonly ap-plied by grapegrowers. And yet, in spite of widespread usage, the chemical and physical nature of nitrogen fertilizer and its effect on grapevine physiology are not well understood by many growers. The University of California has found that a large percentage of California vineyards have nitrogen levels that are either higher than necessary for normal growth or potentially toxic to a vine. In the past, when nitrogen fertilizer was inexpensive, applica-

tion cost was low and winery standards for acceptable fruit quality were less stringent, the economic impact of a poorly-conceived nitrogen program was small. Today, however, the grapegrower is faced with %rising fertilizer costs and lower prices from wineries for grapes that fail to meet current stricter quality requirements. Because both nitrogen deficiency and nitrogen excess may

contribute to reduced yield, poorer fruit quality and lower cash returns, it is essential that the grower be familiar with the fac-tors that affect nitrogen uptake and utilization by the grape-vine. The vineyard operator with a clear understanding of

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Simplified Nitrogen Cycle

k,ss to the atmosphere

vartous ntInkgen inputs plant uptake (decavtng (name matter; nitrogen-carrying raintall and Water; terttlizers)

nucrobtal Khan

Amrnomum Nitrate Nitrogen gas

) en

( NO,) (NO,.) 7— ,N 2 ) triter

leaching loss below the root zone

these factors will be able to develop a cost-effective nitrogen fer-tilization program. In this discussion, we will examine the interaction of various

nitrogen fertilizers with the soil, water and the grapevine. Di-agnosis of vineyard nitrogen status and the types of fertilizers and methods of application will also be reviewed.

Nitrogen and the Soil Nitrogen is taken up by grapevines from sources in the soil.

Of the many forms of nitrogen that exist, only the nitrate (NO3-) and ammonium (NH 4 +) ions are absorbed by the roots of vines. Although vines can utilize either of these forms of nitrogen for normal growth, most of the nitrogen taken up by the plant is in the nitrate form. This occurs for two reasons. First, nitrate is mobile in the soil because it has a negative

charge. Ammonium, on the other hand, has a positive charge which causes it to be held by magnetic attraction (adsorbed) by the negatively charged soil particles. This adsorption renders most of the ammonium unavailable to the plant, while nitrate exists as an available ion in the water found between the soil particles. Secondly, under certain temperature, moisture, and aeration

conditions, the ammonium form of nitrogen is converted by soil micro-organisms to the nitrate form. In fact, all forms of nitrogen are eventually converted to nitrate by these microbial soil organisms. There are many reactions that occur in the soil involving

nitrogen and soil micro-organisms, and the sum of these reac-tions make up the nitrogen cycle, illustrated here . We see that the nitrogen supply in the soil is in constant flux. Grapevines respond to the addition of nitrogen above the

levels usually found in nature. From a practical standpoint, the grower wants to add enough nitrogen in the form of chemical fertilizer to bring the amount in the soil to an optimallevel for \Niiii

healthy growth and crop production. Ideally, this addition is done so that the nitrogen is available at proper levels when the grapevine has its greatest need for it, and in such a way that losses of nitrogen are minimized for greatest cost-effec-tiveness. Individual soils vary in their ability to supply nitrogen to the

vine. Soil physical factors such as aeration, presence of hard-pan, claypan, bedrock or water table, and texture greatly deter-mine the effective root zone. Within this root zone, the cation exchange capacity (CEC— a measure of a soil's ability to adsorb nutrient elements), the available moisture and the abundance of nutrient elements determine the extent to which the vine's roots will utilize the available soil volume. In order for a root to absorb nitrogen, it must come into con-

tact with the nutrient. The nitrogen may move to the root car-ried by water, or the root may grow to the site of the nutrient. Because newly-initiated roots are most effective in absorbing mineral nutrients, much nitrogen uptake occurs through young roots, often called rootlets. Tiny roots penetrate the soil seeking moisture and nutrients,

and have a brief effective lifespan. Many of them die back, and are replaced by new rootlets, much in the same way that the above-ground portion of a vine discards older leaves while producing new ones. As long as moisture in the soil during the growing season permits root growth, the vine continues to de-velop new rootlets, encountering nutrient elements in the proc-ess. However, new roots will not develop in soils that do not have available water.

Nitrogen and Water Water plays an important role in the movement of nitrogen

through the soil. It is with the downward movement of water that the nitrogen reaches the root zone of the vine. Fertilizers

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consisting of the nitrate form of nitrogen will move with the soil water. With excessive water, such nitrogen may ultimately be carried below the root zone. This is referred to as leaching. Fertilizers consisting of ammonium or other positively-charged ions will move downward with water only until an available negatively-charged position on a soil colloid is reached. The ammonium ion is adsorbed by the soil, and further movement is not possible until it is converted into a nitrate by soil micro-organisms.

Available water is required for new root growth, and new root growth is very important for nutrient uptake by the vine. In vineyards where the most practical application method of

nitrogen fertilizer is by broadcasting onto the soil surface, a negative effect of moisture must be considered. Volatilization loss to the atmosphere occurs when ammonium-containing nitrogen fertilizer in contact with the soil surface becomes wet. The nitrate portion is not, however, susceptible to this kind of loss. All ammonium-containing fertilizers are volatile to some extent. Losses of up to 40% of the total nitrogen applied are possible in a very short period. Insofar as possible, the broadcasting of nitrogen fertilizer

should be scheduled so that rainfall or irrigation water will im-mediately carry the nitrogen into the soil, safe from volatiliza-tion loss. Research indicates that the volatility of nitrogen fer-tilizers is especially great on acid soils.

In order to avoid leaching losses, fertilizer application must be timed so that anticipated irrigation or rainfall will carry the nitrogen into the root zone. In making this decision, the grower will be greatly assisted by knowledge of the typical rainfall pattern for the area and the waterholding capacity of the soil. Vineyard soils hold between 3/4" (sandy soils) to 1 1/2" (fine-

textured soils) of available water per foot of depth. An inch of water will move to a depth of between 8 and 16 inches. Usually, the effective root zone is from one to six feet in depth, in the absence of other soil factors. With determinations made for a given vineyard, the timing of

the application attempts to anticipate the amount of rainfall that will occur, with the goal of placing the nitrogen in the root zone at the time when the vine will require a supply for the growth cycle. In irrigated vineyards, nitrogen may be applied along with ir-

rigation water. The grower should calculate the movement of the nitrogen in a similar way, as just discussed, with the goal of delivering the nitrogen into the root zone to coincide with the vine's need for it.

Nitrogen and the Grapevine The need for nitrogen is greatest during the period of rapid

vegetative growth early in the season, when rapid synthesis of vital plant compounds places a large demand on available sup-plies of nitrogen. Grapevine nitrogen levels are highest just prior to bloom. The level of nitrogen in the tissue drops rapidly as vegetative growth slows near bloom and fruit set. Because nitrogen is needed for protein production, chlo-

rophyll synthesis, nucleic acid formation and enzyme synthe-sis, a deficiency reduces total growth of the vine. Reduced growth can mean less foliage, an imbalance of sugar and acid in the ripening fruit, and lower yield. Individual grape varieties differ in their level of nitrogen ac-

cumulation (PW p.26-32 May/June 1985). In an unpublished trial, the University of California found that bloomtime levels of 37 varieties tested ranged from 136 ppm nitrate-nitrogen all the way up to nearly 2,500 ppm nitrate-nitrogen. (J.A. Cook, personal communication). All varieties in the trials were judged by other indicators to be at good nitrogen levels. The influence of rootstock on yield and petiole nitrate levels

has been well-documented. A six-year University of California study of three rootstocks and 22 scion varieties in Naiaa,Valley

showed that rootstocks vary in their ability to provide nitrogen to the vine. Rootstock AXR 1 gave the highest yield and had intermediate

nitrate levels. Variety 99-R was the weakest stock, lowest in Yield and nitrate, but was the most efficient fruit producer per unit of growth. St. George produced the highest petiole nitrate

in seasons that favored high nitrate accumulation, St. George had excessive amounts which were inversely correlated with yield. The research suggests that the erratic performance of St. George in some vineyards was related to its nitrate be-havior. Alternating periods of warm and cool weather, particularly in

the spring, may cause changes in the metabolism of nitrogen in the grapevine. White deposits consisting of the salts of amino acids are occasionally produced along the edge of the leaf during cool periods, and this is an indication of high nitro-gen levels.

Diagnosing Vineyard Nitrogen Status A number of diagnostic methods are available to the grower

for the development of a good nitrogen fertilization program. Correlating the results from these diagnoses, the grower can tailor the fertilizer program to suit the exact conditions in that vineyard. Specifically, the grower should collect information in the following areas:

1) Soil type— What is the cation exchange` capacity of the soil? What is the water-holding capacity of the soil? This indicates

'how water will move in the soil and how well the soil will sup-port root growth.

Do impediments in the soil profile exist which will limit root development and water and nitrogen movement? What is the volume of the root zone? Use this to calculate the

zone in which nitrogen is to be placed.

2) Vine fac — Does the rootstock promote or restrict nitrate accumulation? Is the variety a high, intermediate or low accumulator of

nitrate? 3) Fertilization history of the vineyard— Can current vineyard conditions be correlated to previous fer-

tilization practices? 4) Observation—

Vineyard appearance and yield are important indicators of the nutrient status of the vine: How does the yield compare with normal for the variety and

the location? What is the level of vegetative growth, and how does this

compare with other vineyards in the area? Tissue symptoms can be important clues to nutritional problems: Is the foliage low in color, with low vegetative growth and

yield? These together might indicate low nitrogen levels. Do white deposits of the salts of amino acids occur along leaf

margins during cool spells in early spring? Correlated with high vigor and low yield, these factors might mean excess ni-trate levels.

5) Petiole analysis— Analysis of plant tissue is an essential part of mineral nutri-

tion diagnosis. Properly collected samples are chemically ana-lyzed and the results are interpreted, taking into account sea-sonal differences, rootstock and variety. Depending upon vineyard location and weather of a given season, full bloom usually occurs in May or early June. Varieties differ in their pe-riod of bloom, so a grower may have to sample at different times.

In order to insure accuracy, a large enough number of petioles must be collected. These are chosen randomly, taking a petiole from a leaf that is next to a duster, and discarding the leaf blade

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Comparison of Nitrogen Fertilizers

'Type % Nitrogen $1lb Nitrogen• Volatility Acid-Forming

Ammonium nitrate 34 $.4211b low yes

Ammonium sulfate 21 $.45/1b low yes

Calcium nitrate 15.5 $.70/lb no no

Urea 46 $.35/lb high yes

•Based on typical retail prices in California, Fall 1985

immediately. Usually a minimum of 100 petioles is collected from a block no larger than 10 acres. A paper bag is used to col-lect the samples, so that there is good air circulation. Use of plastic bags can promote development of microbial growth on the sample tissue, distorting the laboratory results. . The samples should be delivered to the laboratory as soon as possible, but may be stored in open paper bags until delivered. Drying does not affect the accuracy of the analysis. For a detailed discussion of petiole analysis, please refer to Grapevine Nutrition and Fertilization published by the University of Cali-fornia. There is potential for error in petiole analysis in several steps of the process. By understanding these steps, the grower can make the most of his sampling results.

First is sampling error in the vineyard. Areas of different soil types should not be mixed in one sample, and the sample size should be sufficient to overcome individual plant variation. Second is time of collection. This is probably the greatest source of error in petiole analysis, because the level of nitrate drops rapidly from a high prior to full bloom. Judging the exact time of full bloom is often difficult, so the numerical result of the sample may not be precisely the full bloom level of nitrate upon which standards are based. Third is contamination, either before collection from vineyard

sprays, or afterwards before delivery to the laboratory. Finally, utilize a dependable laboratory.

Types of Nitrogen Fertilizer Nitrogen fertilizers are produced in a number of common for-

mulations. Too often, one is chosen only on a cost-per-pound of nitrogen basis. There are other considerations, as discussed above, which can give the grower a specific reason to choose another formulation. Occasionally, a grower might have a specific reason to choose another formulation. For example, in acid soils, calcium nitrate might be used to counter the low pH; or, the relative mobility of the nitrogen might suit a particular timing or method of application.

Comparison of Nitrogen Fertilizer Of the commonly used fertilizers, urea and those with nitrate

formulations are mobile in the soil. Those with ammonium formulations are adsorbed, and only become mobile after microbial transformation to nitrate. Urea is especially subject to volatilization. Various granular and liquid preparations are available, depending on the type of application method used.

Application Methods Common ways of applying nitrogen fertilizer include broad-

casting, banding and spot placement; sub-surface placement; and injection into irrigation water. All surface applications of ammonium-containing formulations should be timed to coin-cide with rainfall or irrigation in order to minimize volatiliza-tion. Incorporation of these materials into the soil reduces potential loss. If nitrogen is to be injected into irrigation water, the amount of water applied should be calculated to move the nitrogen into the root zone.

Summary Nitrogen contained in the soil is dynamic in nature, cons-

tantly changing in form and availability. The best use of nitro-gen will be determined by yield response and fruit quality, petiole analysis, and the observations and knowledge of the grower. Although nitrogen fertilization is only one aspect of a comprehensive management system, it has a wide -reaching impact on the health, productivity and profitability of a vineyard.

References Christensen, L.P., A. Kasimatis, F. Jensen, 1978. "Grapevine

Nutrition and Fertilization in the San Joaquin Valley." Univer-sity of California publication 4087. Cook, J.A. and L. Lider. 1964. "Mineral Composition of

Bloomtime Grape Petiole in Relation to Rootstock and Scion Va-riety Behavior." Proceedings of the American Society for Hor-ticultural Science, Vol.84: 243-254. Reisenauer, H.M., ed. 1978. Soil and Plant-Tissue Testing in

California. University of California Bulletin 1879. Soil Improvement Committee, California Fey tilizer Associa-

tion. 1980. Western Fertilizer Handbook. Interstate Printers & Publishers, Inc.

Winkler, A.J., et al. 1974. General Viticulture. University of Cal-ifornia Press.

SCHEMATIC PATHWAY OF NITROGEN IN GRAPEVINES

PRO

Nitrate (NO3)--->

amino <----giufami other

acids

reductase light

warm tern

enzymes

ps. carbohydrates

ammonium 4_ glu6mic (NH4) 'acid

NO3

Z' amino acids

PROTE

Changed by bacteria to atmospheric N (denitrification)

?a . 3

fu

Ammonium N

(NH; )

/ / ao

O

12-

\It

Nitrate N (NO;)

Electrical fixation

Combustion fixation

Removed from cycle by harvesting

Industrial fixation

Legume fixation

Nitrogen fertilizer

• Soil

Animal uptake

Soil

i Plant

up ake

Organic nitrogen in soil organic

matter

//1

than

9ed to nitrate b••I Removed

by leaching

C op residues

The nitrogen cycle.

Some soil organisms especially important in the nitrogen cycle. (Left to right) Azotobacter, nitrate bacteria, and nodule organisms of alfalfa.

NITROGEN NUTRITION AND VINE CANOPY MANAGEMENT

Peter Christensen, Extension Viticulturist U. C. Kearney Agricultural Center

Nitrogen (N) fertilization is a key factor toward promoting and managing an effective leaf canopy in table grape vineyards. The goal is to fully utilize the trellis system for optimum photosynthesis without unnecessary leaf shading within the canopy.

N deficiency is generally not a problem in table grape vineyards. Most are receiving at least adequate amounts of N. However, excess N is not uncommon and can contribute to adverse effects, especially with certain varieties and trellis systems.

To understand N's role in vine canopy management, let's review its pathway in grapevines. Much of this knowledge of N in grapevines has been developed by Dr. Mark Kliewer at U. C. Davis.

Most of the N compounds in the soil, whether from ammonia, urea, or organic sources, are eventually converted to the nitrate form by soil organisms. Nitrates are absorbed by vine roots and moved with the transpirational stream through the xylem to the leaves. There they are converted to amino acids which are the protein building blocks. Amino acids move to the vines' growth and storage areas, such as fruit, shoots, and roots, where they are formed into proteins for growth or become stored N, mostly as the amino acid arginine. Many complicated biochemical steps are involved, but the major ones are shown in the following diagram.

These reactions help us to understand certain vineyard problems associated with high N levels.

Spring N Build-up

This is a weather-related condition found in vineyards of moderately high to very high N levels. It is more common in young, vigorous vineyards, especially of Thompson Seedless, Cardinal, Ribier, Italia, and Muscat of Alexandria. Vine foliage levels of nitrates, ammonium, and amino acids temporarily build-up to high levels. White, salt-like deposits of amino acids (glutamine) appear on the leaf edges where they remain after being exuded through pores (hydrathodes) on the leaf edges. Direct toxicity from ammonium and/or nitrate can occur in extreme cases, resulting in a water-soaked appearance and burning of leaf tissue. Also, an excessive shatter or burning of flower clusters prior to and during bloom is sometimes associated with N build-up, particularly in Cardinal and Muscat of Alexandria. The symptoms are temporary, lasting about 2 to 5 weeks, with the vines ultimately resuming normal growth.

N build-up is associated with one or several cycles of alternating warm and cool periods in the spring. It seems logical that it is caused by reduced N conversion rates in the leaves during cool and sometimes cloudy weather. Low light and temperatures reduce the rate of enzyme and photosynthetic activity involved in N's pathway. Individual grape variety differences in susceptibility may be explained by their inherited differences in potential N-reducing enzyme activity.

L oo

Petiole nitrate levels associated with this condition in Fresno County are as follows:

Nitrate-N, ppm

1700 and above Amino acid exudate deposits may occur. 3500 and above Toxicity symptoms, including leaf burn, may occur. 8300 Highest level found in severely affected Cardinals. 8800 Highest level found in severely affected Thompson Seedless.

These symptoms and their associated nitrate levels vary widely with variety and season. For example, nitrate-N levels up to 7200 ppm have been found in petioles with no leaf burn--only amino acid exudate.

The extreme symptoms described here are not common. Usually, the only visual indication of a temporary N build-up is the presence of amino acid deposits on leaves.

Extreme or High Vigor

This is the most common problem related to high N. A reduced fruit set is some-

times associated with an extreme rate of vigor. However, the more common effects include excessive shading within the leaf canopy and poor cane selection at pruning. Many shoots are of excessive diameter and internode length; they will tend to be of poorer maturity at dormancy.

Lower bud fruitfulness is especially a problem in Thompson Seedless where the dense canopy contributes to a high percent of "shade canes." "Shade canes" are those which developed mostly in the shaded interior of the canopy. They have been demonstrated to have a lower percent bud break, percent fruitfulness, and poorer cluster development as compared to "sun canes." "Sun canes" are those which develop from shoots with leaves exposed to full sunlight on the outer part of the vine foliage canopy.

The problem of cane selection in vigorous Thompson Seedless vines seems to be compounded when they are headed low ("crowned low") under a high, wide "T" trellis or a double trellis. Renewal shoots for next year's canes must then grow 21/2 to 31/2 feet from the head where they originate to reach full sunlight on the vine canopy's exterior.

Thus, at least this lower portion of all fruiting canes are somewhat shaded during their period of fruit bud development the previous growing season. Also, only so many leaves can occupy the space provided on the canopy's sunny exterior. Therefore, excess growth merely produces more shoots to shade one another.

Obviously then, N fertilization should be geared mainly to vine growth and vigor needs. A basic rate is 40 to 60 lbs. of actual N/acre. An additional 20 to 30 lbs./acre may be needed to support grass culture or to compensate for leaching losses in sandy soils. Vines with root problems or old Emperor vines may need up to 100 lbs./acre to encourage growth.

Caution against excessive N is especially needed in fertile, deep fine sandy loans. Also, the nitrate content of well waters should be determined by an experienced commercial laboratory and taken into consideration in N programs.

APPLY NITROGEN CORRECTLY

For maximum uptake of nitrogen, proper timing of application is important

By Gary A. Couvillon and C. H. Hendershott

N ITROGEN fertilizer is too expen-sive to waste. Howeve ► many

fruit growers may be doing exactly that applying it at the wrong time. even

if they are following their state rec-ommendations.

Recommendations for time of nitro-gen application to fruit plants are con-fusing and vary considerably from state to state. In many cases, recommenda-tions concerning the time of nitrogen application to fruits do not correspond to data relating to time and conditions of maximum nitrogen uptake.

Nitrogen is highly soluble in water, and must be applied at times when ni-trogen uptake by the plant is taking place. If it is applied at other times it is often lost due to leaching through the soil profile or run-off. •

Narrow Uptake Periods The entire root system including the

large older suberized roots are capable of nutrient absorption. The rate of ab-sorption is greatest in the newly pro-duced "white roots" (root tips). Thus, the period of greatest nutrient uptake would coincide with the period of maximum root growth, since there should be the greatest amount of "white roots" at this time. This period varies with locale and fruit species, but generally would be from March through October.

Leaves are also necessary for effi-cient nitrate uptake. Nitrate uptake is very low from the period of leaf fall to the commencement of shoot growth the following spring. Nitrate uptake in-

Both authors are with the Department of Horticulture. University of Georgia. Athens. GA 30602.

creases with shoot elongation and re-mains high until leaf fall. It is also known that the later nitrogen is ap-plied during the season the less it is used the year of application, and the greater is its contribution the next year.

Stored nitrogen during the dormant period (February) was highest (20% greater) in trees that received August nitrogen applications when compared to March applications. It has also been shown that the nitrogen content of apricot blooms was 34 fold greater when nitrogen was applied late in the previous summer.

Stored N Important It was concluded that nitrogen had

to be applied prior to leaf fall in order for it to reach reproductive organs by bloom. Thus nitrogen applied late in the year is stored (primarily in the root system) for use the following year.

Nitrogen is accumulated in plant tissue according to the supply during the year. It is utilized for growth and flowering the following season irre-spective of the nitrogen supplied dur-ing the winter or spring in question.

Thus, nitrogen utilized during bloom and the period of rapid shoot elongation following bloom is de-pendent upon the redistribution of stored nitrogen from the previous year's application. However, during late spring or early summer, shoot growth becomes dependent upon the external nitrogen supply. All stored nitrogen was found to be exhausted by the end of June.

When one takes all of these factors into consideration it becomes clear that nitrogen must be applied during pe-riods of active uptake or one may ex-pect excessive nitrogen loss due to leaching. The nitrogen utilized in the fruit plant in early spring comes pri-

marily from stored reserves from nitro-gen application during the previous summer or fall. Nitrogen utilized in late spring and summer comes primarily from current season's nitrogen appli-cations.

Apply in Fall and Late Spring Thus, an application of nitrogen in

the fall of the year should build up the stored nitrogen reserves for the follow-ing spring. A second application in middle to late spring (not early spring or late winter) should be sufficient to supply the nitrogen needs of the tree during spring and summer.

Care should be taken not to overfer-tilize trees with nitrogen during the late spring or early summer. The result could be delayed fruit maturity and poor fruit color. Nitrogen application during this period should result in less nitrogen loss and more efficient utili-zation when compared to nitrogen ap-plications during the dormant period (i.e. 6 weeks before bloom). This rea-soning seems to hold true for other woody plants and supports the data that show the beneficial early season effects of fall nitrogen applications over dormant season applications.

Fruit species with low chilling re-quirements are not in a deep state of growth inhibition at the end of sum-mer. Thus, nitrogen application could result in vegetative regrowth. Because of this problem nitrogen application to these species should be delayed until October or following the first day in the fall that the temperature drops to 40°F. These plants are inhibited by this time to such an extent that regrowth will not occur. Since peaches, pears. apples. etc. have a long rest period, they generally are in deep rest by late September. Ni-trogen application at this time should not result vegetative regrowth. ❑

f\A ‘va v) D 32

Late-fall nitrogen application in vineyards is inefficient

William L. Peacock ❑ Francis E. Broadbent ❑ L. Peter Christensen

fr) E

G rapevines are fertilized with nitrogen (N) in amounts intended to promote proper shoot, leaf, and berry development and to provide for maturation of the crop. The need for N is greatest during rapid shoot growth in the spring through the berry development stage, then diminishes after mid-summer when ripening begins. Application should be timed to ensure an adequate N supply during spring development, but available N in late summer should not be high enough to en-courage late-season shoot growth, delay maturity, and promote immature canes. Fer-tilizer N should also be used to maximize uptake efficiency and minimize losses by volatilization and leaching. Immediate incor-poration of all ammonic fertilizers can greatly reduce volatilization. Appropriate timing of nitrogen application and avoiding over-application of water can decrease leaching and denitrification.

Fall application of nitrogen fertilizer in the San Joaquin Valley is convenient for the grower and has increased in popularity in re-cent years. It allows better use of time and labor, and the grower can take advantage of lower fertilizer prices when working condi-tions in the vineyard are good. It has been assumed that N applied in the late fall re-mains in the root zone over the winter and is

available for use by the plant when it breaks dormancy the following spring. This assump-tion is based on the relatively low winter rain-fall of the southern San Joaquin Valley, but experimental data to support it are lacking.

A study to evaluate the relative leaching and denitrification losses of late-fall and spring applications of N to vineyards was conducted in 1979-80 at two locations, one in Fresno County on Delhi sand and the other in Tulare County on Greenfield sandy loam. Delhi sand is a wind-deposited soil with a deep, uniform, well-drained profile. Green-field sandy loam absorbs water readily, but drainage is impeded by a hardpan at 4 feet. Both vineyards are in mature Thompson Seedless grapes produced for raisins.

A randomized complete block design was used with five blocks and three treatments. Plots, with four vines each, were 12 by 24 feet. Treatments consisted of the unfertilized control, 100 pounds N per acre applied No-vember 9, 1979, and 100 pounds N per acre applied March 12, 1980. The fertilizer was "N-depleted ammonium sulfate, isotopically labeled to permit distinction between fertil-izer and soil nitrogen. It was applied in a 6-foot strip on each side of the row by a hand-held boom on a backpack sprayer and then incorporated by disking. Distribution of

inorganic N in the soil was followed by sampling the profile to a depth of 4 feet in in-crements 0 to 0.5, 0.5 to 1, 1 to 2, 2 to 3, and 3 to 4 feet. Soil cores were taken from four locations in each plot, and the cores compo-sited for laboratory analysis. Soil samples were taken from the Delhi location on De-cember 4, 1979, and on April 11 and May 23, 1980. Sampling dates at the Greenfield site were December 6, 1979, and April 13 and May 23, 1980. Soil samples were immediately frozen and stored in a freezer before analysis. In the laboratory, inorganic N, consisting of ammonic and nitrate forms, was extracted and the isotopic composition determined to identify the portion derived from the added fertilizer.

N concentrations in soils As expected, with no fertilizer application,

inorganic N concentrations in the Delhi sand profile remained low at all sampling times and did not vary greatly with depth (fig. 1). During the 25 days between the November fertilizer application and the December 4 sampling, 0.70 inch of rain fell. The Decem-ber sampling reflects the November fertilizer application: no appreciable leaching had occurred. By April II, 1980, however, when 10.7 inches of rain had fallen since the No-vember fertilizer application and the grower had applied an additional 3 to 4 inches of water for frost protection, all evidence of the November fertilizer application had disap-peared. In the case of the March-applied fer-tilizer, which had received 0.34 inch of rain and 3 to 4 inches of irrigation water, the April 11 sampling revealed a surface inorganic N concentration somewhat lower than the max-imum observed with the November applica-tion to this soil. By May 23, even the spring application had disappeared. Presumably all the fertilizer N applied in March had been ab-sorbed by plants or leached below 4 feet.

The Greenfield-sandy-loam location re-ceived approximately the same amount of rainfall as the Delhi site. Vines were irrigated for frost protection in the last week of March, and two additional irrigations total-ing 8 to 12 inches were applied before the May 23 sampling. Inorganic N after the November fertilizer application was high near the sur-face on December 6, but by April 13 concen-trations were not much different from those of the control soil. By May 23, concentra-tions had increased a little in the surface 2 feet because of mineralization of soil N as temper-atures increased. In the case of the March application, the April 13 sampling reflected the recent addition of fertilizer to the soil. By May 23 some downward displacement of this

22 CALIFORNIA AGRICULTURE. JANUARY-FEBRUARY 1982

1- 3

DELHI SAND

Inorganic N, ppm

'''10 20 30 40

No Fertilizer 4,, November Fertilizer

Fig. 1. Inorganic nitrogen concentrations in Delhi sand plots. . ,"4 • P. -1-7.4" F‘.-.'..r";, 4 0.;s: 7,1_4e ' ' '

--1GREENFIELD SANDY LOAM •

Ar-i':..1norganic N, ppm 20 30 40 50

,.

0-40 December 6,1979 , •

April 13,1980 •

Fig. 2. Inorganic nitrogen concentrations in Greenfield sandy loam plots.

Macr hi Fertilizer

Fig. 3. Inorganic N from fertilizer as affected by treatment and sampling time. r

fertilizer had clearly occurred, but most of the N remained within the surface 4 feet of soil.

Fertilizer-derived N Figures 1 and 2 reflect the combined fertilizer and soil N present in the profile. Figure 3 shows concentrations of fertilizer-derived N, calculated on the basis of isotopic data. In Greenfield sandy loam, high concentrations of November-applied fertilizer were present in the December sampling, whereas by April and May most of this N had disappeared. Fertilizer applied to this soil in March was displaced downward between the April and May samplings.

In the Delhi soil the concentration of fer-tilizer N in the surface 6 inches of soil receiv-ing a November application decreased from 22 parts per million (ppm) on December 4 to less than 1 ppm by the following April. Where Delhi sand received fertilizer in March, some leaching had occurred by April, and by May 23 fertilizer N throughout the profile had dropped to a very low value.

Discussion These data indicate that ammonic nitrogen

applied in the late fall was subject to severe leaching losses by normal rainfall and irriga-tion between November and May. Soil tem-perature was not low enough during the winter to retard nitrification significantly. This study suggests that N should be applied in the spring just before frost-protection ir-rigation on loam or sandier soils. Subsequent irrigation will leach the N into the root zone for uptake during the most critical period of need. On very sandy soils, such as the Delhi sand, it would be useful to split the fertilizer

... application, with half applied in March and the remainder in May.

Still unanswered is the question of the value of early-fall application (September to mid-October), when the vines may be active enough to take up a significant amount of N and store it in canes, trunk, and roots.

William L. Peacock is Farm Advisor, Coopera-tive Extension. Tulare County, Visalia; Francis E. Broadbent is Professor of Soil Microbiology, Department of Land, Air, and Water Resources, University of California, Davis; and L. Peter Christensen is Farm Advisor, Fresno County.

I

IMPORTANCE •Potassium (K) deficiency in California vineyards is considered third in overall importance, following that of nitrogen and zinc. This is somewhat surpris-ing, because the potassium needs of the grapevine are relatively high and are comparable to the de-mand for nitrogen. The reasons are, in part, the greater initial supply of K in most California soils and resistance of K to losses from leaching. K de-ficiency is usually confined to small areas in a vine-yard—seldom larger than 1 to 3 acres. When vines are deficient, however, the poorer vine growth and lower crop yields can be,dramatic.

K-deficient areas in San Joaquin Valley vine-yards probably total no more than several thousand acres. The deficiency has not been found in Kern County vineyards and is rare in Tulare County, where it may be found only in scattered areas be-tween Kingsburg and Orosi. Fresno County has scattered areas of localized deficiency, mostly east of Dickenson Avenue north of Fresno and east of Highway 41 south of Fresno. In a tissue analysis survey of 120 vineyards throughout Fresno County, only one vineyard was found to be deficient in K, further demonstrating the infrequency and localiza-tion of the problem. K deficiency is rarg in Madera County. Merced and Stanislaus counties have scat- tered deficient areas centering around Ballico, Cres-sey, and Delhi, and around Keyes and Ceres. In San Joaquin County, deficiency is occasionally found in the vineyard areas around Manteca, Ripon, and Escalon.

SOURCES IN THE SOIL

Most K in soils is derived from minerals, notably micas and feldspars. These minerals are only slightly soluble and are usually found as large-size particles. Under the influence of various weathering factors, K is gradually solubilized and becomes available to plants as positively charged ions, which become attached to clay colloids or to organic matter in the soil.

A comparatively large quantity of K is found in soils, but most of it is present in relatively insol-uble compounds. Thus, the available K level in the root zone is a more important consideration than the total supply. The ordinary range of total K in miner-

als ranges from 0.15 percent in sands to 4 percent and higher in clay soils.

When K fertilizer is applied to the soil, part is fixed in slowly available compounds. The extent of fixation is proportional to the amounts and kinds of colloids in the soil, being greatest in clays and clay loams and smallest in sands. K fixation or holding by the soil is important, because it serves as a check against rapid leaching and provides a more continu-ous supply of available K. Even when K fertilizer dissolves in the soil moisture, it is soon attracted to the surfaces of the colloidal complex and replaces sodium, calcium, or some other element associated with the colloidal soil particles. K so fixed may move slowly in the soil, the rate dependent on the amount and nature of the colloidal complex.

The K cycle is fairly simple. It is fixed by the soil; removed by crops and, to a minor extent, by drainage water; exported by harvested crops; and returned to the land in crop residues, manures, or K fertilizers.

K levels are generally highest in the topsoil. Hence, deficiency is most likely to occur in cut areas from land leveling where the less fertile sub-soil is exposed. K deficiency is also more common in sandier soils.

ROLE AND UTILIZATION

Not much is really known about the function of K in grapevines. Much more is known about what happens to vine growth and crop yields when this element is deficient.

Plants need K for the formation of sugars and starches, for the synthesis of proteins, and for cell division. K also neutralizes organic acids, regulates the activity of other mineral nutrients in plants, acti-vates certain enzymes, and helps to adjust water relationships. It increases the oil content of certain fruits, and contributes to cold hardiness. Even though it is considered essential for the formation of carbohydrates and is somehow involved in other processes, it is not usually found as a part of organic compounds. About 1 to 4 percent of a plant by dry weight is K.

The demand for K is highest in midsummer to late summer, when greater amounts accumulate in the ripening fruit. Thus, temporary K deficiencies are sometimes associated with overcropping.

DIAGNOSIS OF DEFICIENCY

The ability to recognize and identify symptoms of K deficiency is extremely important; response to K fertilization has been obtained only in vineyard areas with visible symptoms of deficiency. Fertilizer trials in vineyards with low, but not deficient, levels of K in leaf tissue have not shown a yield or growth response.

Symptoms

Leaf symptoms usually begin to show in early sum- mer and typically are seen first on leaves on the middle portions of the shoots. A fading or yellowing of leaf color begins at the margin or outer edge of the leaf.

As the season progresses, the yellowing contin-ues to progress intp the areas between the main veins, leaving a central island of green extending somewhat along the main veins. (See fig. 3a.) The yellowed leaf areas of colored grape varieties may bronze or redden (fig. 3b). In all varieties, marginal burning and curling, either upward or downward, usually follows. Leaves above and below the mid-shoot section become affected as the season ad-vances, until many of the leaves show some symp-toms by harvest time.

When K deficiency is severe, shoot growth is markedly reduced, and symptoms may be present on nearly all of the leaves before blossoming time. Leaves may drop prematurely, especially if the vines are carrying a heavy crop or-ate stressed for moisture. If leaf drop is extensive, the fruit may fail to develop full color or to ripen normally.

Symptoms of a mild K deficiency do not appear until late summer, approaching harvest. Here, symp-toms may appear on many of the leaves on lateral or secondary shoots. In Thompson Seedless, the late symptoms produce a more blotchy or irregular pattern of chlorosis, particularly on the leaves near the ends of lateral shoots.

Vines severely deficient in K tend to have fewer and smaller, tight clusters with unevenly colored, small berries. With Thompson Seedless the lower portion of the bunch may collapse by midsummer, resulting in raisined, immature berries by harvest. (See fig. 4.)

Much of the effect of K deficiency on the fruit is the result of reduced vine growth and premature leaf fall, and accounts for lower vine yields and fruit maturity. Fruit symptoms alone are not always dis-tinctive enough to be used in diagnosis; other fac-tors, such as moisture stress, water berry, or red berry, can affect the fruit in a somewhat similar manner.

K deficiency symptoms may be confused with those caused by midsummer moisture stress during hot weather. Moisture stress, however, causes a general leaf burn of an irregular pattern that is most prominent on the older, basal leaves. The gradual fading or yellowing pattern, characteristic of K de-ficiency, is not seen.

A high water table during the spring and early summer may induce typical K deficiency symptoms. In fact, many other conditions that substantially reduce the effectiveness of the root system may also cause deficiency symptoms to appear. The diagnos-tic procedure should include digging and careful examination of the vine root system for the presence of phylloxera, nematodes, or unfavorable soil con-ditons.

Vineyard areas showing deficiency symptoms should be marked during the growing season. This will pinpoint the vines to be treated during the dor-mant season.

Using laboratory analysis

Even though keen observers may readily identify K deficiency by means of leaf symptoms, laboratory analysis of a properly collected sample of petioles may verify the diagnosis or help clear up confusion with other disorders. Based on fertilizer trials and field observations, tissue potassium values may be interpreted to determine whether the vines have an adequate level.

Soil analysis is not a reliable means of determin-ing whether a vineyard requires K treatment. Too many variables are involved: the wide range of soil depths; the varying concentrations of K in the soil profile; the many different grape varieties and root-stocks used; and the many factors influencing root health and thus K uptake.

A note of caution: the K level in the vines may be influenced by other conditions that reduce the effectiveness of the roots —overcropping, shallow-rooting, high water table, inadequate irrigation, or heavy nematode or phylloxera feeding. The appli-cation of K fertilizer cannot be expected to give a positive vine response under such conditions.

FERTILIZER PRACTICE

Research results in California for both fruit trees and vines have shown that, when a deficiency exists, massive rates of K fertilizer are necessary to obtain vine or tree recovery and yield response. Large amounts of fertilizer are needed to overcome the high fixation of K in most California soils. Fertilizer mixes or complete fertilizers are not recommended,

8

0

Materials

The symbol "K," used for the element, is from the Latin word for potassium —Kalium. When expressed as a plant food by the fertilizer industry, potassium is usually reported in terms of the oxide, K 20, also called potash.

Potassium fertilizer is commonly available in three forms, each with a different potassium content: ■ Potassium chloride (KC1, muriate of potash)-52

percent K (62 percent K 20) ■ Potassium sulfate (K 2SO4, sulfate ' of potash)-

44 percent K (53 percent K 20) ■ Potassium nitrate (KNO 3)-37 percent K (44 per-

cent K 20) plus 13 percent total nitrogen Studies in Fresno County vineyards have

shown that one fertilizer fdrm offers no advantage over another in terms of vine response, provided . that equal amounts of actual K are used. Thus, the choice will depend on relative cost and availability of the materials and on soil and vine conditions.

Currently, potassium chloride is the most eco-nomical source of K. It must be used with caution, however, because its chloride content might con-tribute to salt injury of vines under some conditions. For example, potassium chloride should not be ap-plied to vineyard soils with an existing salinity con-dition, nor should it be used on shallow or poorly drained soils. It is best used during the dormant season and should be avoided during spring and summer. Only a low to moderate rate applied during the winter is safe for young vines.

Potassium chloride can be used safely on well-drained soils without a salinity problem. One or two heavy furrow irrigations directly over the area treated are recommended as the best means of reducing the concentration of chloride fertilizer. It is somewhat dangerous to rely on rainfall alone to move the fertilizer, because rainfall amounts are not likely to be adequate. Light rain might be ex-pected to leave a slightly dispersed, but still con-centrated fertilizer band in the root zone. To leach the chlorides in sprinkler-irrigated vineyards, one should also provide some irrigation in excess of the grapevines' water needs.

The relatively high cost of potassium nitrate all but eliminates its use in vineyards as a soil treat-ment. Potassium sulfate is slightly more expensive than potassium chloride, and is safe to use during the dormant season. However, it should be used with some caution during the growing season, es-pecially on young 'vines, because experience with this form is limited. Thus, from a practical standpoint,

Rates

A high rate is needed to overcome the high K-fixing power of most San Joaquin Valley soils. (See table 3.) The quickest response by far can be achieved by applying the fertilizer in a single heavy applica-tion rather than in small amounts applied annually. In general, the speed and degree of vine recovery, as well as the length of effectiveness, improve as rates are increased.

TABLE 3. SUGGESTED POTASSIUM APPLICATION RATES, BASED ON SEVERITY OF DEFICIENCY

Application rate

Per vine Per acre equivalent*

deficiency KCI K2SO4 KCI K2SO 4

lb lb lb lb Severe

4 - 4'/z 5 - 6 1,800 - 2,000 2,300 - 2,700 Moderate

31/2 4 1,600 1,800 Mild

2 1/2 3 1,150 1,350

*Pounds per acre equivalent is based on 454 vines per acre (8' X 12' spacing).

Application methods

Deep placement of K fertilizer in a concentrated band close to the vine is recommended for most soils. This places the fertilizer near the root zone and also is the best means of overcoming soil fixa-tion.

The fertilizer can be applied by hand or banded with a fertilizer applicator into the bottom of 6- to 8-inch-deep furrows opened about 18 to 24 inches from the vine on each side of the row. Many growers have found a 1-pound coffee can a convenient mea-sure for applying K fertilizer by hand. A level, full can holds almost exactly 3 pounds of potassium sulfate.

Open French (row) plow furrows can also be used. In either case, the furrows should be left open to allow rainfall and irrigation water to move the fertilizer. The first irrigation should be made in these furrows to ensure deeper movement.

On sandy soils, surface banding of 2 1/2 pounds of potassium sulfate on each side of the vine row (total of 5 pounds per vine) was successful in limited studies in Fresno County vineyards; movement into the soil depends on winter rainfall. The vines responded fairly rapidly after surface applications, presumably because of a good concentration of actively growing roots near the soil surface in the

. Vine

the choice of a potash fertilizer narrows to either potassium sulfate or potassium chloride.

because they have a relatively low K content and hence would be needed in unreasonably large amounts to supply enough K.

9

6

spring. Use of this method should be limited until more experience is gained; only high rates of potas-sium sulfate have been evaluated.

When subsoiling is done reasonably close to the vine rows, K fertilizer may be placed in the subsoiler slots. Good vine responses have been observed following such applications.

Foliar sprays. Potassium nitrate applied in foliar sprays in extensive Fresno County trials has shown no promise in correcting deficiency. During the growing season, repeated sprays at 4 to 5 pounds of potassium nitrate per 100 gallons of water did not measurably increase tissue K levels or reduce deficiency symptoms over a 3-year test period. Higher rates could not be used because of toxicity to young leaves.

Time of treatment

The late fall or early winter is a good time to treat, allowing maximum exposure to winter rainfall to help move the fertilizer into the soil. At the latest, the fertilizer should be applied before the first irrigation in early spring, before bud break. Some growers have found that an application in the fall

is convenient, because deficient areas can still be defined by the presence of leaf symptoms.

Symptoms are not corrected immediately after fertilizer application in the winter. A partial improve-ment in leaf color or in vine growth may not appear until midsummer; a full response usually is not attained until the second growing season, or even the third, after fertilizer treatment.

Treatment longevity

A single application of K fertilizer at a recommended high rate will sustain an adequate K tissue level and eliminate leaf symptoms for 5 years, at least. Typically, the treatment loses effectiveness after about 8 years. Higher rates than those in table 3 can last for 10 years and beyond. If soil pests, such as nematodes or phylloxera, are causing root prob-lems, the longevity of any treatment can be ex-pected to be shortened.

It would be prudent to observe the treatment area closely for reappearance of foliar symptoms and to monitor the tissue level of K by collecting petiole samples for laboratory analysis. This procedure will be helpful in anticipating the time when a follow-up fertilizer treatment may be necessary.

Grapevine Nutrition and

Fertilization in the San Joaquin Valley

Vt- Y's1 eV+)

2

0

O

0 0

0

0 0 0 0 0

O ° 0 0 0 0

0 O 0

O Potassium and ammonium ions

0 0

0 0

`474: 2:1-type silicate clay layer

10%

I IN SOIL SOLUTION

1 4/V.4 NONEXCHANGEABLE EXCHANGEABLE

POTASSIUM POTASSIUM

FERTILIZERS POTASSIUM MINERALS

EROSION LOSSES FIXATION

LEACHING LOSSES

CROP - REMOVAL

0

0

O

0

0

O 0

0 Other smaller cations (H', Ni , Ca", etc.)

Clay minerals of the 2:1 type such as illite have the ability to fix ammonium and potassium ions. Smaller ions. such as H. Na , and Ca' can move in and out of the internal adsorption surface and arc thus exchangeable. Potassium and ammonium ions arc of such size as to fit snugly between crystals, thereby holding them together. At the same time, these larger ions are rendered at least temporarily non-

exchangeable or fixed.

RELATIVELY UNAVAILABLE POTASSIUM

(FELDSPARS, MICAS, etc.) 90-98% of total potassium

4 SLOWLY AVAILABLE

POTASSIUM

(NONEXCHANGEABLE (fixed) ) 1-10% of total potassium

READILY AVAILABLE POTASSIUM

(EXCHANGEABLE and SOLUTION) IN SOIL

1-2X of total potassium

Gains and losses in available soil potassium under average held condi-tions. The approximate magnitude of the changes is represented by the width of the arrows

Relative proportions of the total soil potassium in unavailable, slowly available, and readily available forms. Only Ito 2 percent is rated as readily available. Of this, approximately 90 percent is exchangeable and only 10 percent appears in the soil solution at any tune/

CROP RESIDUES, , COMMERCIAL SLOWLY AVAILABLE MANURES

•21•30131450:1•

IIRIONLIGEMIOROHO es.

MICRONUTRIENTS

IMPORTANCE

Zinc (Zn) deficiency has been recognized as a prob-lem in California grape production for more than half a century. Known as the little-leaf disease, it was first identified and corrected as a nutrient defi-ciency by Chandler and his co-workers in the early 1930s.

Zn deficiency, the most widespread micronu-trient deficiency of grapes in California, ranks second to nitrogen deficiency in the number of acres involved. An estimated 10 to 20 percent of California vineyards and orchards are affected, and 20,000 or more acres of grapevines show varying degrees of Zn deficiency. It is common in' most of the San Joaquin Valley where grapes are grown, rare in the viticultural areas in the north coast coun-ties, and fairly common in vineyards grown in the central coastal region.

SOURCES IN THE SOIL

Zn is found in minute quantities in all soils; sandy soils have the lowest levels. After being weathered from various minerals, Zn is adsorbed by clay par-ticles and by organic matter and is held in an ex-changeable condition. Zn levels tend to be higher in surface soils and often accumulate after being released by decomposing leaves and other plant material.

Zn is less available in soils with a pH greater than 6. At lower pH values, the nutrient becomes more soluble and available. Virtually all of the Zn in the soil becomes fixed at pH 9.

Calcareous materials, such as limestone, in-crease the Zn-fixing capacity of coarse-textured soils. Soils high in organic content and clay soils of high magnesium content are often low in avail-able Zn. Soils high in native phosphate also may fix Zn in an unavailable form.

Deficiency symptoms are commonly found in San Joaquin Valley vineyards grown on sandy soils and on sites previously used for long periods for corrals or poultry houses. Zn deficiency is also common in vineyards grown on sandy soils with vigorous rootstocks, such as Dogridge, Salt Creek, Harmony, and Couderc 1613, where nematode resistance is needed.

12

Zn deficiency is not usually encountered uni-formly across a vineyard, but is found in limited areas such as sand streaks. Areas subject to heavy cuts during land leveling are likely to be deficient in Zn, as are sandy soils that have received repeated, heavy applications of poultry manure for long periods.

Application of high-nitrogen fertilizers may accentuate zinc deficiency, because nitrogen stim-ulates total vine growth and thereby increases the Zn needs beyond the available supply. Likewise, vigorously growing young vines, especially in their second year, commonly show temporary and usually mild Zn deficiency due to rapid growth and a still limited root system.

Zn deficiency is very common where grapevine cuttings are planted in methyl-bromide-fumigated soils, such as in nurseries. This results from the temporary reduction of the mycorrhyzal fungi popu-lation, which assists roots in the uptake of certain nutrients, including Zn and phosphorus.

ROLE AND UTILIZATION

Zn is needed for auxin formation, for the elongation of internodes, and in the formation of chloroplasts (chlorophyll-containing bodies) and starch. In grapes, Zn is essential to normal leaf development, shoot elongation, pollen development, and the set of fully developed berries.

DIAGNOSIS OF DEFICIENCY

Symptoms

Foliage. Deficiency symptoms may vary, depend-ing on the degree of the shortage and on the grape variety. Foliar symptoms of mottling usually appear in early summer at about the time that lateral shoot growth is well developed. The new growth on both the primary and secondary shoots has smaller, somewhat distorted leaves, with a chlorotic pattern exposing the veins as a darker green color. Even the small veinlets retain a uniform-width border of green unless the deficiency is quite severe.

In contrast to normal leaves, which have a deep sinus or cleft where the petiole is attached to the blade, severely affected leaves have undeveloped

2 1 0

basal lobes; the sinus is shallow, showing little or no indentation. (See fig. 6.) The term "little leaf" aptly describes the gross appearance of stunted shoots, which have closely spaced, small, distorted leaves when deficiency is severe. Some varieties, such as Rubired and Royalty, may have leaves with wavy margins in addition to a distinct veinal pattern.

Fruit. On grapevines Zn deficiency can seriously affect the set and development of the berries. This leads to reduced yields or to lowered acceptability of table grapes. Vines deficient in Zn tend to pro-duce straggly clusters with fewer berries than do normal vines. The berries usually range in size from normal through small to very small (undeveloped, or shot). In seeded varieties, the small and shot berries have fewer seeds than normal berries, rang-ing down to none in the very small shot berries. Shot berries often remain hard and green and fail to ripen, but this symptom varies considerably. (See fig. 7 and 8.)

Varieties like Muscat of Alexandria are particu-larly sensitive to Zn deficiency, and development of straggly clusters with berries of various sizes is one of the first effects seen. Leaf symptoms on this variety develop only when the Zn deficiency is more extreme. Thompson Seedless, Carignane, French Colombard, and Tokay, however, always have some degree of foliar symptoms associated with fruit symptoms. The Cardinal, Ribier, and Red Malaga varieties of table grapes respond much like Muscat of Alexandria. Salvador, on the other hand, often shows moderately severe leaf symptoms with-out an effect on berry set.

Laboratory analysis

Fortunately, Zn deficiency symptoms on leaves and fruit are distinctive and readily recognizable; thus, tissue analysis is usually not needed for diagnosis. However, laboratory analysis for Zn may be used for questionable symptoms, because other micro-nutrient deficiency symptoms and those of certain virus diseases, such as fanleaf, can sometimes be confused with Zn deficiency.

Soil analysis for Zn content is not a reliable method of determining a vineyard's need for Zn. It is difficult to correlate Zn level in the soil with that in the vine because of differences in the suscepti-bility of grape varieties to the effects of low Zn, differences among rootstocks in Zn uptake from the soil, and the extensive "feeding" nature of grape root systems that enables a vine to maintain a satis-factory Zn level even though the soil content may be considered low. Because the Zn level in the grapevine reflects all of these variables, tissue analysis is preferred over soil analysis.

SUPPLYING THE GRAPEVINE'S NEED FOR Zn Once a Zn deficiency has been diagnosed, there are several methods of treating vines with Zn. One method may be better adapted than another to a specific vineyard situation.

Daubing For spur-pruned varieties, the most common and successful treatment is to daub or paint all fresh pruning cuts with a solution of zinc sulfate. To im-prove uptake and prevent "washing" away of the Zn solution, pruning must be timed so that little or no bleeding occurs.

Vines usually do not bleed if pruned between December and early February. However, if the soil moisture is low and the vines are "dry," pruning and daubing should be postponed until after a soaking rain or a winter irrigation. Pruning and daubing also should be delayed during periods of cold, desiccating winds or unusual, prolonged cold spells. Under these unfavorable conditions, vines may absorb the Zn solution in amounts that damage the buds and spurs.

Best results are obtained when the pruning cuts are made about V2 inch above the uppermost node and are daubed as soon as possible after pruning, preferably within 3 or 4 hours. Delays of 8 to 12 hours reduce entry of the Zn solution, because gums are produced, plugging the wood.

The recommended concentration is 1 pound of zinc sulfate (36 percent metallic Zn content) in 1 gallon of water; a higher concentration may cause injury. The solution should be made by slowly add-ing the zinc sulfate to the water, stirring rapidly to ensure immediate and complete solubility. Usually 2 to 4 gallons of solution per acre are sufficient. Food coloring is sometimes 'added as a means of checking the thoroughness of the dauber.

A short stick padded on one end with a sponge or absorbent cloth is used to daub the vines. One worker can usually keep pace with three or four pruners by walking back and forth between rows.

Instead of daubing, some growers spray the zinc sulfate solution at the same concentration on the spurs, using less than 100 pounds pressure. To be effective, full rows of vines must be pruned out within several hours. Although this technique has not been studied, reports of commercial success indicate that it is worthy of trial, especially on larger vineyard acreages.

Foliar sprays Even though daubing is successful on spur-pruned varieties, it is not effective on cane-pruned varieties, because a smaller number of cut surfaces can be

■ 13

treated and the movement of Zn in the vines is lim- ited. Thus, on cane-pruned varieties, such as Thompson Seedless, foliar sprays are normally used.

Foliar sprays may also replace daubing in vine-yards of spur-pruned varieties when Zn deficiency is mild. In cases of severe deficiency, it may be advisable to apply a foliar spray in addition to the daubing treatment.

Zn sprays should be applied 2 or 3 weeks be-fore bloom (late April or early May) if an improve-ment in berry set is desired. The vines should be sprayed with enough volume to wet the flower clusters and the undersurfaces of the leaves. One spray application is usually sufficient. If foliage symptoms persist or reappear later in the growing season, a second application may be needed.

Those who wish to mix their own spray material can add 4 pounds of zinc sulfate (36 percent Zn) plus 3 pounds of spray lime to 100 gallons of water. The spray lime is used as a safener to prevent leaf burn. A suitable wetting agent should be included to ensure complete wetting of the flower clusters

•-• and leaves. A number of spray materials containing up to

50 percent Zn are available under various trade names and can also be used effectively by following the label recommendations. They have been neu-tralized to prevent foliage burn and are often re-ferred to as basic zinc sulfates.

Chelated Zn materials can also be used in foliage sprays but, to date, have been less effective on a label-recommended and on a cost-per-acre basis than the basic zinc sulfates. However, Zn chelates may be preferred in concentrate or low-volume spray application; they are fully soluble in the spray tank. Basic zinc sulfate is not fully soluble and requires good agitation to remain in suspension with a more concentrated tank mix. Also, more at-tention must be given to occasional flushing of sprayer lines because of possible settling of the material.

Recent research results indicate that a full-wetting application with a dilute sprayer (100 to 150 gallons per acre, prebloom) results in more zinc absorption than a concentrate-sprayer application (20 to 30 gallons per acre) when comparable rates of Zn per acre are used. Thus, the choice of applica-tion method and type of material may depend on the degree of deficiency —a dilute application of basic zinc sulfate being the most effective and therefore preferable for the more serious problems.

Some vineyardists use unneutralized zinc sul-fate (36 percent Zn) alone, rather than mixing it with lime or using basic zinc sulfate. They use a maximum rate of 11/2 to 2 pounds zinc sulfate per 100 gallons water to avoid foliage burn. Before using this technique, the grower should test it on limited acreage.

24

Usually Zn is the only nutrient needed as a vine foliar spray. Adding other nutrients, such as phos-phorus, has not improved the effectiveness .of Zn sprays in Madera and Fresno County vineyard trials. Also, it is not advisable to sacrifice an optimum amount of Zn in the spray tank to include other nutrients commonly found in proprietary foliar nutrient mixes.

Soil applications

Success with soil applications of zinc sulfate has been limited to sandy and sandy loam soils. Such applications probably should be confined to small, chronically deficient areas or to soils where spraying or daubing of vines has not been effective or prac-tical. Because most soils fix large quantities of Zn, deep placement and high rates are required.

During the dormant season, a concentrated band of zinc sulfate can be placed in 8- to 10-inch-deep furrows about 18 inches on each side of the vine row. To concentrate the material, the bands should be only 2 to 3 feet long beside each vine, and they should be left exposed so that irrigation will move the material into the soil. The suggested rates are 1 pound per vine for young vines and 2 to 3 pounds for mature vines.

Zn EDTA chelates have also been used success-fully with furrow applications at rates of 1/2 to 1 ounce elemental Zn per mature vine. However, on a cost-per-acre basis, the chelates are usually no more effective than zinc sulfate.

Hand soil injection

Another means of deep soil placement is to inject a zinc sulfate solution 18 inches deep into the soil with a hand gun attached to a spray rig, using a pressure of about 250 pounds per square inch (psi). Injections should be made no closer than 1 foot from the vine trunk, and only during dormancy.

For young vines up to 3 years old, a rate of I/2

to 1 pound of zinc sulfate per vine can give com-plete correction. Severely deficient mature vines may require 2 to 3 pounds per vine. A suggested concentration of the injected solution is 100 pounds zinc sulfate per 100 gallons water. The rate per vine is calibrated by timing the flow rate from the hand gun into a measured bucket.

Fresno County studies have shown that hand injection of zinc sulfate solution results in greater response than does furrow application, when equal rates per vine are compared. Soil applications by either means may be effective for 2 or 3 years; re-treatment usually is necessary.

2 (Z

Shank injection in continuous bands Shank injection of Zn solutions is not as effective as the aforementioned methods. It does not provide as concentrated a placement near individual vines and therefore requires even higher rates of Zn fertilizer for deficiency correction.

However, this method can be practical in nur-sery rows with their more concentrated plant den-sity. Shank injection is a common practice in nursery soils planted to grapevine cuttings where a methyl

• bromide fumigation has induced a Zn deficiency. This temporary deficiency can be largely corrected by shank-injecting a Zn chelate solution on each

side of the nursery rows to an 8- to 10-inch depth. Five pounds or more of elemental Zn per acre in chelated form are required.

Other methods Other corrective measures that have been investi-gated for grapevines include injection of zinc sul-fate solution under pressure directly into vine trunks, application of zinc sulfate dust in dusting sulfur, driving metallic Zn points or galvanized nails into vine trunks, and late fall or dormant season zinc sulfate sprays. None of these methods has been as effective or considered as practical as the daubing or spraying techniques described.

Boron (B) IMPORTANCE Boron (B) is unique among the micronutrients be-cause of the narrow range of soil B levels between deficiency and excess (toxicity). A fraction of one part per million in the soil solution is all that is re-quired for sufficiency, and several parts per million can be toxic. This section covers deficiency prob-lems; problems of excess B are covered in the section on toxicity problems.

B deficiency in California vineyards was first recognized in the mid-1950s in widely separated areas —in San Bernardino County in southern Cali-fornia, in five San Joaquin Valley counties (Tulare, Fresno, Merced, Stanislaus, and San Joaquin), and in the coastal region, including Santa Clara, Napa, Sonoma, and Mendocino counties.

In the San Joaquin Valley, deficiencies have been noted primarily on the more sandy, alluvial soils of granitic origin on the east side of the valley extending from northern Tulare to San Joaquin County. This is particularly true of soils associated with the original flood plains or alluvial fans of the Kings, Merced, or Stanislaus rivers. Vineyards irri-gated primarily with canal water originating in the Sierra Nevada are subject to deficiency, as are those receiving well water of very low B content.

Even in those areas, B deficiency is not exten-sive—occurring mostly on sandy soils, in low spots, or near irrigation valves where excessive leaching with irrigation water occurs. However, because B deficiency can drastically affect fruit set and vine growth, and the cost of treatment is relatively low, B fertilizer application is warranted over entire vineyard blocks that have a deficient spot, or as insurance against deficiency in general areas known to be low in B.

Soils on the west side of the San Joaquin Valley were mostly derived from sedimentary materials, which generally provide larger amounts of available B than do the soils on the east side.

SOURCES IN THE SOIL Native B is mostly in the form of borosilicate min- erals, which are resistant to weathering and release B slowly. Much of the available B is held by the organic and clay fraction in the soil through com-plexing and anion adsorption. Thus, it is less leach-able than are other neutral or negatively charged plant nutrients.

UPTAKE, UTILIZATION, AND ROLE B is taken up by plants as 'borate and functions in the differentiation of new cells. With B deficiency, cells may continue to divide, but the structural parts are not properly or completely formed. B also regu-lates the carbohydrate metabolism in plants. In the grapevine, low B limits pollen germination and normal pollen tube growth, thus reducing fruit set.

B does not move to young leaves from older ones in plants, and thus deficiency is first found in the youngest tissues of the plant. A continuous supply is necessary for normal growth.

DIAGNOSIS OF DEFICIENCY

B deficiency symptoms are fairly complex and de-pend on the severity and the time of year during which they occur. Some symptoms can be easily confused with those of other disorders. Generally,

25

B deficiency can be separated into two categories: a temporary, early-spring deficiency and early-to-midsummer deficiency.

Temporary, early-spring deficiency The symptoms—stunted, distorted shoot growth—appear after bud break; then most of the shoots begin to elongate normally by late spring. The symptoms are much more widespread in some years, particularly following a fall and early winter of very low rainfall.

Although the reason for this relationship is not well established, the most widely accepted explan-ation is that it is a temporary, drought-induced B deficiency. In many crops, dry soil conditions can temporarily induce a boron deficiency. Thus, it is believed that a drought-induced deficiency during the preceding fall and early winter may affect nor-mal cell development in the maturing buds. As the shoots emerge Ithe following spring, B deficiency symptoms appear. Symptoms are more likely to appear in areas of poor soil moisture conditions, such as in shallow soil. There is also a wide range in the degree of symptoms among individual vines within an area. Shoot symptoms. The shoots are dwarfed be-cause of the abnormally short internodes, which may grow in a zigzag manner. (See fig. 9.) Numer-ous lateral shoots grow from the stunted shoots, giving a bushy appearance. The growing tip may die on severely affected shoots; affected shoots are unfruitful or have underdeveloped clusters.

Because late spring growth usually becomes normal, the symptoms are confined to early growth. Leaf symptoms. The lower leaves on affected shoots are misshapen, but symptoms differ among varieties. For example, severly affected Grenache leaves are somewhat fan-shaped and may show an interveinal chlorosis; the serrations around the leaf edges are irregular, and the veins are more promi-nent than on normal leaves. Affected Chenin blanc leaves have a wide, fan-shaped appearance and prominent veins. White Malaga leaves are partic-ularly crinkled; Barbera and Mission leaves have a more rounded but misshapen appearance.

Early-to-midsummer deficiency This condition occurs more consistently from year to year than does early-spring deficiency. The symp-toms usually appear in May and June. The most serious and common effects are on berry set and development, resulting from insufficient vine B levels during the period of rapid growth from sev-eral weeks before bloom until several weeks after-wards., Unless quite deficient, the vine will have adequate B levels again by midsummer and will continue normal growth.

Fruit symptoms. Fruit symptoms are the easiest to recognize. Severely affected vines may have no crop. Some clusters appear to burn off or dry around bloom time, leaving only cluster stems, sometimes with occasional berries.

Many clusters may set numerous small, seedless berries that persist and ripen. These clusters may be full or straggly and may also include some normal-size berries as well as shot berries. (See fig. 10.) The shot berries are distinct and uniform in size and shape. Unlike the more oval or elongated normal berries of most varieties, the shot berries are very round to somewhat flattened, resembling in profile a very small tomato or pumpkin. (See fig. 11.)

Shot berries caused by low B level should not be confused with those caused by zinc deficiency. Clusters from zinc-deficient vines have shot berries of normal shape, typical of the variety, and most of these berries remain hard and green. They also are more varied in size than are those caused by B deficiency.

Occasionally, in B-deficient vines, clusters that appear to set at bloom time shatter severely at about midsummer. Leaf and shoot symptoms. Foliar symptoms usu-ally do not appear until late spring or early summer. Obvious symptoms are always accompanied by pronounced fruit symptoms, because pollination and fruit set are the physiological processes of the grapevine most sensitive to low B levels at that time. On affected leaves, a mottled fading of green color develops into yellow areas between veins. The more advanced chlorotic areas may show some burn. (See fig. 12.)

The leaf chlorosis pattern of B deficiency may be confused with that of black measles. However, B deficiency symptoms occur primarily on younger leaves, whereas black measles equally affects older leaves. Also, the presence of clusters with purplish black, speckled berries is an obvious symptom of black measles.

Some shoot tips stop growing and die. The result is lateral shoot development, some of which may be stunted for a while but, within a few weeks, resumes normal growth. By midseason, this new growth may hide the early-symptom leaves and stunted growth. In cases of severe deficiency, brown lesions may appear on the internodes, which, when cut lengthwise, reveal hollow, brown areas in the pith.

FERTILIZER PRACTICE

Instructions on using B fertilizer should be followed closely, because higher than recommended rates can cause toxicity.

Vineyard blocks with only a few vines showing symptoms should always be treated to avoid un-

26

predictable increases in symptoms in some years. Also, normal vineyards in susceptible, B-deficient areas can be treated as insurance against possible deficiency. The degree of susceptibility to defi- ciency can be verified through bloom-time petiole laboratory analysis for B levels.

ti t. ,

Materials o

A number of B fertilizer materials containing dif-ferent amounts of actual B are manufactured. The fertilizer industry expresses B content as percent boron trioxide (B 2 O3 ). Common borax, which con-tains 34 percent B 2O 3, can be used; other boron materials specifically used as fertilizers range from 44 to 68 percent B 2 O 3 . They vary from granular or coarse to fine powder and also differ in solubility. Any material is satisfactory for direct soil application, but only a finely ground B spray material should be used for application in water.

Rates

Materials containing 34 to 48 percent B 2O3 should be applied at 1 ounce per vine, or 25 to 30 pounds per acre. Two-thirds ounce per vine, or 20 pounds per acre, is recommended for materials containing higher concentrations of B.

Application methods

Small vineyard blocks can be easily treated by hand-broadcasting the material 1 to 3 feet from the trunk of each vine. A shot glass or 35mm film canister is a convenient container for application.

The most accurate method of treating larger acreages is to spray the soil. This is because standard fertilizer application equipment cannot be cali-brated to apply the recommended small rates of B.

For soil spray application it is necessary to de-termine the desired gallons per acre and then dis-solve the correct amount of a boron spray material into the tank. For example, 38 pounds of boron spray material (50 percent B 2O 3 ) per 100 gallons of

water applied with a spray rig calibrated at 50 gal-lons per acre will give 19 pounds borax material per acre, or 2/3 ounce per vine, on an 8- by 12-foot vine spacing. The spray should be directed toward the irrigation furrow area to ensure fertilizer movement into the root zone.

Some growers avoid an extra operation by merely adding B to the vine-row herbicide spray treatment applied in early winter. The only disad-vantage of this method is the dependence on rain-fall to move the material to a sufficient depth during the first year.. •w :,31-11v

Soil applications can also be made with a vine-yard duster by calibrating the duster to the recom-mended pounds per acre and directing the nozzles toward the ground. Only the fine and medium grades of B fertilizer are recommended for duster application. The finely ground spray powders drift too easily when applied with a duster.

Aircraft have been successfully used to apply the coarse or granular B materials on large acreages.

Foliar sprays of B can be used as an intermed- iate treatment at rates up to 4 pounds B spray ma- terial per 100 gallons water. However, B soil treat- ment ensures longer lasting correction of deficiency.

• Time of treatment B fertilizer can be applied any time, preferably be-fore an irrigation. A fall or early winter application provides for maximum exposure to winter rainfall to help move the fertilizer into the soil.

Treatment longevity

Treatments have been known to last up to 8 years and more. However, re-treatment is recommended every 5 years in B-deficiency-prone vineyards, un-less laboratory tissue analysis or tie recurrence of symptoms dictates otherwise.

A convenient B fertilizer maintenance method is to apply half the recommended rate every 3 years in combination with a vine-row herbicide spray treatment.

TOXICITY PROBLEMS- EXCESS BORON it& SALINITY

Boron (B)

IMPORTANCE

A more widespread potential exists for excess boron (B) than for deficiency in the San Joaquin Valley. Each type of B problem exists in distinctly different, separated geographic areas. As previously men-tioned, B deficiency is found on the east side of the San Joaquin Valley on soils of granitic origin and those irrigated with water low in B content (below 0.1 ppm). In contrast, soils on the west side of the Valley, from Kern through Stanislaus County, are mostly derived from sedimentary materials, which commonly provide greater amounts of available B. For example, a number of soils in western Kern County have been found to contain over 10 ppm B in the subsoil, with levels up to 98 ppm B (in sat-urated extract).

The underground water supply in many west side areas contains excess B, which has been one of the greatest limiting factors in the development of vineyards in that part of the San Joaquin Valley. This limitation is gradually changing with the impor-tation of canal water via the Delta-Mendota Canal and the California Aqueduct. The availability of this good quality (low B) water may reduce problems in some areas to those caused by the level of B remain-ing in the soil profile in existing and potential vine-yard sites.

TABLE 4. GENERAL GUIDELINE FOR GRAPEVINE SENSITIVITY TO SOIL B

Grapevine symptoms and effects

none possible, very slight slight moderate severe very severe

*In saturation extract.

30

SOIL B AND GRAPE VARIETY

Grapevines are among the crops classified as sensi-

tive to excess B. Soil analysis can be used as an indicator of this hazard. (See table 4.) Soil samples should be taken in increments down to a 5-foot depth at least, because B levels vary in the profile and are often higher in the subsoil.

There are obvious differences among grape varieties in tolerance to B. This has been evaluated in commercial and experimental plantings in west-ern Fresno County since 1968. The effects have varied with cultural and irrigation practices, vine vigor, and soil type. Generally, the most tolerant of the varieties evaluated is French Colombard. White Malaga, Grenache, and Emerald Riesling are also in the tolerant category.

Varieties of intermediate tolerance include Tinta Madeira, Carignane, Ruby Cabernet, Emper-or, Cardinal, Barbera, Zinfandel, Rubired, Cabernet Sauvignon, Perlette, and Petite Sirah. The per-formance of Chenin blanc, Royalty, and Thompson Seedless places them in this group, even though they usually show higher tissue levels of B. Cal-meria, Souza°, Alicante Bouschet, Muscat of Alex-andria, and Orange Muscat are among the least tolerant varieties.

Weak vines and those under moisture stress are most seriously affected.

SYMPTOMS AND EFFECTS

B tends to accumulate along the leaf margins until the concentration becomes sufficiently high to be toxic to the leaf tissue. The effects usually appear first on the older leaves as a dark brown to black discoloration, or necrosis, on the very edges of the leaf margins at the tips of the serrations.

The necrosis progresses inward as numerous dark brown specks, which can become almost con-tinuous around the leaf margin (fig. 17). They also develop toward the center of the leaf between the primary and secondary veins.

zip

Soil B*

ppm 0 - 0.5 0.7 - 1.0 1.0- 1.5 1.5 - 2.5 2.5 - 4.0

above 4.0

If B excess appears while the shoots are still actively growing, the young expanding leaves cup and wrinkle, because expansion of the leaf edges slows or stops and the middle part continues to grow. (See fig. 16.) Necrotic specks may also de-velop along the leaf margins on the deformed leaves.

AVOIDING AND CORRECTING EXCESS B excess can be avoided simply by not planting in problem areas. Grapevines should never be planted where the irrigation water source contains 1 ppm B and above. Even with a supply of good quality wa-ter, vineyard establishment should be delayed until soil B levels are lowered by leaching to near 1 ppm or below. Some leaching can be accomplished after vineyard planting, but often this goal loses its priori-ty to other tasks in vineyard management and water

needs of other crops in the farm operation. Sprink-ler irrigation is the most effective method of water application for leaching. Flood irrigation requires more water and time. Furrow irrigation is the least effective, especially in existing vineyards with only two furrows between 12-foot rows.

Some of the B in soils is not readily soluble and thus is not as easily removed by leaching as are chlorides and sulfates. Up to 8 to 10 acre-feet per acre of water are required to leach excess B levels in badly contaminated soils —that is, to reduce 10 ppm B levels to 1 to 2 ppm. This is approximately three times the amount of water required to remove excess chloride from saline soils.

Generally, fine-textured soils fix more B and thus take longer to reclaim. Those with dense sub-soils, such as Merced and Oxalis soil series, are very difficult to leach and should never be considered for grapes when they contain excess B.

Sodium (Na) and Chloride (Cl) Sodium (Na) and chloride (Cl) problems are usually encountered simultaneously.

Damaging levels of Na or Cl are associated with soils that are sodic (alkali), saline (excess salts), or both.

SODIUM EXCESS

Soil permeability problems

An appreciable percentage of the Na in the soil is found on the cation exchange complex, where, like potassium and magnesium, it is attached to negative-ly charged clay particles and organic matter. Soils that contain excessive amounts of exchangeable Na in proportion to calcium and magnesium are termed sodic soils—more commonly called alkali soils.

Sodic soils are characterized by a dispersion of soil particles, which reduces a soil's permeability to water and air. The laboratory determination for the Na hazard of soils is the exchangeable Na per-centage (ESP). This gives a close approximation of the degree to which the soil exchange complex is saturated with Na ions and is rated for vineyards as shown in table 5.

Sodic soils are reclaimed by displacing the exchangeable Na with soluble calcium, usually by adding gypsum (calcium sulfate) and leaching.

Toxicity to grapevines

The principal effects of excess Na on grapevines are caused by soil physical and permeability prob-

lems. However, grapevines can also accumulate fairly high levels of Na from strongly sodic soils. The direct effects of a Na excess in plant tissue are not always clear, because excess Na is most commonly associated with excess chloride uptake as well.

The leaves also can directly absorb toxic levels of Na during sprinkler irrigation with poor quality water. Water containing over 3 milliequivalents per liter (me/1) of either Na or Cl may burn grape leaves when evaporation is high. Damage from such wa-ters can be minimized by restricting sprinkling to nighttime only, when evaporative conditions are lower, and by ensuring that the sprinklers rotate at least once a minute.

The potential for burn increases with increased

TABLE 5. ESTIMATED ESP (EXCHANGEABLE SODIUM PERCENTAGE) AS A MEASURE OF

Na EFFECTS ON SOIL PERMEABILITY

Percentage

Effects on permeability

Below 10

Generally no permeability problem.

10 - 15

Possible permeability problems on clay loam and clay soils.

Above 15

Permeability problems are likely on all mineral soils with the possible exception of sands and loamy sands.

31

2

concentrations of Na or Cl. At 8 me/1 and above, leaf burn is severe, and suitability of the water for sprinkling is questionable, even if restricted to nighttime application.

CHLORIDE TOXICITY TO GRAPEVINES

Cl salts are normally a principal constituent of saline soils, which are defined as those having a soluble salt content great enough to reduce or prevent plant growth. This reduced growth is largely the result of the salts' osmotic effect, which makes water uptake by the roots more difficult.

Saline soils with a relatively low concentration of Cl may have only a moderate osmotic effect on vine growth. However, a predominance of Cl in the same concentration of salts may produce a severe leaf burn due to a direct Cl toxicity. The threshold level for this hazard to grapes is 10 to 25 me/1 of Cl in the soil saturation extract, depending on the grape variety.

Even though grapes cannot tolerate high levels of Cl, separate tests for Cl levels in soils are not suggested. For grapevines, a critical appraisal of Cl levels can be satisfactorily included in a deter-mination of the total salts. Total salts are measured by the electrical conductivity of a soil saturation extract and expressed as millimhos per centimeter (EC e as mmho/cm). Table 6 gives EC e criteria for grapes.

Problems caused by excess Cl are most com-monly associated with saline soilkthat are not fully reclaimed and with poor quality irrigation waters. Water with an EC w (electrical conductivity of irri-gation water) above 1.0 mmho/cm poses problems; severe problems occur at EC w values above 2.7. Toxicity problems of increasing severity can be expected as Cl levels in irrigation water increase above 4 me/1; severe problems occur at levels above 15 me/1. As previously mentioned, more than 3 me/1 sodium or chloride in sprinkler irrigation water

TABLE 6. TOTAL SALTS (EC e ) CRITERIA FOR GRAPES

ECe (average for root zone)

Effect on grapevine

mmho/cm

Below 2.5

2.5 - 4.1

4.1 -6.7

6.7 and above

Grapevines usually not appreciably affected (0% to 10% yield reduction).

May restrict grapevine growth to appreci-able extent (10% to 25% yield reduction). Severely restricts grapevine growth; varying degrees of leaf burn are expected (25% to 50% yield reduction).

Severe effects, including extensive leaf burn and possible vine death.

increases the toxicity hazard from leaf absorption. Other conditions that contribute to excess Cl

salts include poor irrigation management, poor water penetration, restricting soil layers, or a high water table.

VARIETY TOLERANCE TO Na AND Cl

Grape varieties can be placed in general groupings based on their performance under excess Na and Cl conditions in commercial plantings. French Col-ombard and Palomino are among the most tolerant varieties, followed by Grenache, Chenin blanc, and Thompson Seedless in an upper-intermediate tol-erance group. The performance of Emerald Ries-ling, Rubired, and White Malaga places them in the above groups, even though they often show higher Na and Cl tissue levels.

A lower-intermediate tolerance group includes Ruby Cabernet, Gamay, Petite Sirah, Muscat Canel-li, Semillon, Carignane, and Royalty. Varieties with the least tolerance are Muscat of Alexandria, Alicante Bouschet, Italia, Ribier, SouzEo, Nebbiolo, and Barbera.

DIAGNOSIS OF Na AND Cl EXCESS

Reduced vine growth and marginal leaf burn are strong indicators of toxicity caused by Na or Cl or both. The burn appears on mature leaves in mid-summer to late summer. Under severe conditions, the leaf burn begins by early summer, and the vines are quite stunted and may even die. The leaf burn progresses from the margin as an abrupt browning. There is no accompanying chlorosis as with defi-ciencies of K and Mg. (See fig. 18.)

Leaf analysis is extremely useful in diagnosing salt injury to grapevines. Soil and water analysis may be needed to complete the diagnosis and indi-cate the Na or Cl hazard and the need for corrective measures. Backhoe soil observations are also useful in diagnosing accompanying soil profile problems.

CORRECTIVE MEASURES Correcting Na and Cl problems include breaking up restrictive soil layers by ripping or slip-plowing to improve internal drainage, amending soils or irri-gation water or both with such materials as gypsum, changing water supplies, improving water applica-tion, and leaching effectively. Publications covering these practices in detail are available from Univer-sity of California Cooperative Extension county offices.

32

JULY/AUGUST 1999

WINEGROWING

Thomas J. Rice, PhD Soil Science Department California Polytechnic State University San Luis Obispo, CA

Liming vineyard soils to increase soil pH and raise calcium levels has been practiced for centuries in the humid areas of the world where soils tend to be more

acid. Today, liming is increasingly prac-ticed in the semiarid central coast regions of California, where liming of vineyards was unheard of even a decade ago.

Past agricultural practices, such as the addition of sulfur, acid-forming nitrogen fertilizers, and organic soil amendments, have caused soil acidifi-cation. Previously, most of these lands were either open space, range lands, or planted to grain crops.

To avoid unnecessary expense and protect the soil from environmental degradation when lime is used as a soil amendment, growers must assess their vineyards carefully to determine the proper types and amounts of liming materials to add.

What is lime? Generally the term "lime," or "agri-

cultural lime," refers to all limestone-derived materials used to neutralize acid soils, including ground limestone (calcium carbonate; CaCO 3), hydrated lime (calcium hydroxide; Ca(OH) 2), or burned lime (calcium oxide; CaO), with or without additions of magnesium carbonate, magnesium hydroxide, or magnesium oxide. In strict chemical terminology, lime refers to calcium oxide (CaO).

Quick field test for lime To test for the presence of lime in

your vineyard, take a spoonful of soil and drop a few drops of muriatic acid or 10% hydrochloric acid on it. If bub-bling or fizzing occurs (due to carbon dioxide gas, CO2), this indicates the presence of carbonates or bicarbonates (lime). A quantitative determination of soil lime content requires laboratory analysis.

Lime and soil considerations Adding lime increases soil pH,

improves microbial activities, and increases the availability of nitrogen (N) and phosphorus (P). Adding exces-sive lime is expensive and undesirable for many reasons. Although the Cost of lime, resultant yield increases, and increased grape quality determine the net benefit derived, lime is usually a profitable soil additive on strongly acidic (pH below 5.0) soils.

The following three facts about lim-ing soil are particularly important:

• Lime additions generally improve soil structure, especially in clay soils, and in combination with phosphorus, may give larger increases in yields than lime alone.

• Toxic levels of soluble and exchangeable aluminum (Al) can be almost eliminated by raising the pH to between 5.2 and 5.5 with lime; further liming to a pH between 6.0 and 6.5 usually increases yields. The beneficial effects of raising the pH from 5.3 to 6.5 is likely due to an increase in biological activity, which increases the available nitrogen (N), molybdenum (Mo), and calcium (Ca).

• Adding high amounts of lime (raising pH higher than '6.5) may require addition of plant nutrients,

such as iron (Fe), zinc (Zn), manganese (Mn), and phos-phorus (P), which become less available to plants at a pH greater than 7.5.

How much lime to apply To arrive at a satisfactory

solution to the problem of how much lime to apply, the pH requirements of the grape rootstock and scion, the pH and buffer capacity, and cation exchange capac-ity (CEC) of untreated soil

should be considered. The most satis-factory means of determining liming needs is by soil tests. Soil samples should be taken at least every three years.

The lime needs within a vineyard can be interpreted most kaccurately when a detailed soil survey report and map are produced and the various soil series in the vineyard are identified. The soil series descriptions will characterize soil texture, structure, mineralogy, and other root-zone characteristics, such as humus content and permeability, which will affect the lime response.

There is a relationship between tex-ture, CEC, and buffering capacity —resistance to a change in ion concentra-tion. The more clay and organic matter there are in a soil, the more lime is needed to change the pH, because the soil colloids may contain large quanti-ties of exchangeable Al and H ions due to their high CECs.

The amount of pH change desired and the type of clay mineral present also affect the amount of lime needed to change the pH. The relative amount of lime needed in soil of the same initial pH with the following principal clay minerals decreases as we move through the list of vermiculite, montmorillonite, illite, kaolinite, and sesquioxides (metal oxides).

Methods of applying lime If needed, lime can be applied to

advantage at any stage in the establish-ment of a vineyard. It is usually recom-mended to add lime several months ahead of rootstock planting to allow time for resultant pH changes.

Lime is usually applied by spreading it on the soil surface. Newly spread lime should be well mixed at least one

LIMI\ OF VINE S

ZI 0

foot deep, prior to planting of grape vines. On strongly acidic soils, where more than three tons per acre (TPA) of lime are required, half the amount may be applied before soil ripping and the other half applied and disked in after ripping and prior to rootstock planting.

When less than two TPA of lime are needed, the entire amount may be applied and disked in before planting. When both surface soils and subsoils are strongly acidic (pH below 4.5), it sometimes pays to incorporate lime to a depth of at least 12 inches! Lime will not react well in the soil unless it is incorporated into the soil. Therefore, it will not work well in no-till vineyards, but can work well in high rainfall areas with lots of earthworms.

Application depth of liming materials

Surface applications of lime without some degree of mixing in the soil are not immediately effective in correcting subsoil acidity. In several studies it was obsqued thii 16 to 14_years were required for unincorporated, surface-

- applied lime to increase the soil pH at a depth of six inches. For fairly high rates, broadcasting half of the lime at the soil surface and disking the other half is a satisfactory method of mixing lime in the upper foot of soil.

Neutralization of subsoil acidity through deep incorporation of surface-applied lime is possible with the tillage equipment now available. With no-till vineyard systems, where the vineyard cover crop is mowed and not culti-vated, the surface soil pH can decrease substantially in a few years because of the acidity produced by the decomposi-tion of plant residues. Fortunately, the increased acidity is usually concen-trated in the topsoil, where it often can be readily corrected by surface liming.

Time and frequency of liming applications

In vineyards with cover crops that include legumes, lime should be applied three to six months before the time of seeding; especially on very acid (pH below 4.5) soils. Lime may not have adequate time to react with the soil if applied just before the cover crop seeding.

Frequency of application generally depends on the soil texture, N source and rate, crop removal, precipitation patterns, and lime content. On sandy soils, frequent light applications in the. winter are preferable, whereas on fine-textured soils, larger amounts may be applied less often during the rainy sea-son. Finely divided lime reacts more quickly, but its effect is maintained over a shorter period than that of coarse materials.

Lime balance sheet When a soil has had its acidity

reduced (pH increased) by lime, how often must lime be added and how much is needed to keep the soil pH suitable?

The answers depend upon the rate of lime loss. Lime is neutralized or lost from the soil by such activities as:

• Neutralization by acid-forming fer-

tilizers (ammonium-nitrogen; NH4-N), which produces a rapid change.

• Neutralization by the acid formed 1 by carbon dioxide dissolved in water (from air, biological respiration, and organic matter decomposition), which is a slow continual process.

• Leaching of alkaline soil materials below the root zone, such as calcium carbonate, which produces a slow change.

• Removal in harvested or grazed crops, which produces a slow loss.

• Erosion. As topsoil is eroded, more acidic subsoil may be exposed.

Liming materials The anion accompanying any cation

(usually Ca") must lower H' activity in the soil solution. Gypsum (CaSO4 2H20) and other neutral (pH near 7.0) salts cannot neutralize H', as illustrated in the following reaction:

Gypsum (CaSO4 . 2H20) + 2H' <—> Ca' + 2H* + S042 + 2H20

As seen above, the W levels are the same on each side of the equation;

therefore, no pH change has occurred. Liming reactions begin with the neu-

tralization of H' in the soil solution by either OR or HCO3* originating from the liming material. For example, CaCO3 behaves as follows: CaCO3 + H2O —> Ca' + HCO3 + OH" The rate of the reaction is directly

related to the rate at which the OR ions are removed from solution. As long as sufficient W ions are in the soil solu-tion, Ca" and HCO3 will continue to go into solution. When the W ion concen-tration is lowered, formation of the Ca" and HCO3 ions is reduced.

Neutralizing value of liming materials

The materials commonly used for liming soils are Ca and/or Mg oxides, hydroxides, carbonates, and silicates (Table I). The value of a liming material depends on the quantity of acid that a unit weight of it will neutralize, which in turn, is related to the molecular com-position and purity.

Pure CaCO3 is the standard against

1111bIe 'Neutralizing:y*00 forms of ':Soine-

Liming material Neutralizing value */0

CaO

179 Ca(OH)2 136 CaMg(CO3)2 119

CaCO3 100 CaSiO3 86

Source: Western Fertilization Handbook

Agricultural ground limestone** (TPA)`

Soil Buffer

Mineral Soils

Organic Soils'

pH 7.0° 6.5° • 6.0d 5.2

6.8 1.4 1.2 1.0 0.7 6.6 3.4 2.9 2.4 1.8 6.4 5.5 4.7 3.8 2.9 6.2 7.5 6.4 5.2 4.0 6.0 9.6 8.1 6.6 5.1 5.8 11.7 9.8 8.0 6.2 5.6 13.7 11.6 9.4 7.3 5.4 15.8 13.4 10.9 8.4 5.2 17.9 15.1 12.3 9.4 5.0 12.0 16.9 13.7 10.5 4.8 22.1 18.6 15.1 11.6

• Shoemaker, McLean, and Pratt are soil chemists who developed the procedure. ••Agricultural ground lime of 90% neutralizing power (TNP) or CaCO3 equivalent, and fineness of 40% >100 mesh, 50% >20 mesh, and 95% >mesh. ' To convert tons per acre (TPA) to metric tons per hectare, multiply by 2.24. `Because of lower mineral contents, organic soils are often suitable when limed only to pH 5.0 to 5.5.

Desired pH level for the soil.

Source: Soils in Our Environment and Soil Fertility and Fertilizers

36 JULY/AUGUST 1999

WINEGROWING

which other liming materials are mea-sured, and its neutralizing value is con-sidered to be 100%. The calcium -car-bonate equivalent (CCE) is defined as the acid-neutralizing capacity of a lim-ing material expressed as a weight per-centage of CaCO 3.

- 411,

Magnesium carbonate (MgCO3) will neutralize 1.19 times as much acid as the same weight of CaCO 3; hence its CCE is 119%. The same procedure is used to calculate the neutralizing value of other liming materials.

Quality and fineness of limestone Agricultural limestone's effective-

ness depends on the degree of fineness, because the reaction rate depends on the surface area in contact with the soil. CaO and Ca(OH) 2 are powders, but most limestones must be crushed to reduce the particle size and increase the surface area.

Because the cost of limestone also increases with fineness, materials that require minimal grinding, yet contain enough fine material to change pH rapidly, are preferred. Agricultural limestones contain both coarse and fine materials. Many states in the U.S. have laws that require that 75% to 100% of the limestone pass an 8- to 10-mesh screen and that 25% pass a 60-mesh screen. This way, there is fairly good distribution of both the coarse and fine particles.

Fineness is quantified by measuring the distribution of particle sizes in a given limestone sample. The effective calcium carbonate (ECC) rating of a limestone is the product of its CCE (purity) and the fineness factor.

Lime requirement: Different meth-ods have been developed to determine the amount of lime needed to bring the pH of an acid soil to a desirable range. All of those analytical methods

presently used take into consideration the buffering capacity of the soil.

A major problem of managing acid soils is to estimate the quantity of lime required to raise the soil pH to a certain level (see Table II). Non-legumes, such as grapes, can derive nitrogen from nitrogen fixed in legume cover crops. Much of the vine response to liming may actually be the pH responding to nitrogen fixation by the legume-Rhizobium relationship in a cover crop containing legumes.

Although many people still regard the primary effect of lime to be the pro-vision of adequate soil calcium, its main value is really the addition of hydroxyl (01-1. ) ions to the soil solu-tion: CaCO3 + H2O ====> + HCO3 + Off

The hydroxyl ions produced from the lime neutralize soil acidity, raise soil pH, and thus provide the most impor-tant effects of the liming process. Increased quantities of soluble and exchangeable calcium and magnesium are merely by-products of liming, although their greater amounts in limed soils may be beneficial to plants having high calcium requirements, such as legumes, and the increased cal-cium will help improve soil structure.

Conclusion The decision to add lime to increase

soil pH should depend on the goals of the vineyard manager relative to root-stock and scion selection. If lime is to be added, it is best to incorporate it at least one foot deep prior to planting of rootstock.

In established vineyards, there is no economical and effective method to sig-nificantly raise the subsoil pH by lim-ing. The best one can hope for is to raise the pH of the upper six inches of soil and to increase the decomposition rate of any cover crop residue. Therefore, it is best to obtain a detailed soil map and soil test information prior to vineyard establishment to make a wise decision regarding soil liming. ■

References 1. California Fertilizer Association. 1995.

Western Fertilizer Handbook. 8th edition. Interstate Publishers, Inc., Danville, IL.

2. B.D. Doss, W.T. Dumas, and Z.F. Lund. 1979. "Depth of lime incorporation for cor-rection of subsoil acidity" Agron. J. 71(4): 541-544.

3. Himelrick, D.G. 1991. "Growth and nutritional responses of nine grape cultivars to low soil pH." Hort. Science 26: 269-271.

4. Miller, RW., and D.T. Gardiner. 1998. Soils in our environment. 8th edition. Prentice Hall Publ., Englewood Cliffs, NJ.

5. Robinson, J. (editor). 1997. The Oxford companion to wine. Oxford Univ. Press, New York, NY

6. Tisdale, S.L., W.L. Nelson, J.D. Beaton, and J.L. Havlin. 1993. Soil fertility and fertiliz-ers. 5th edition. Macmillan Publ. Co., New York, NY

7. Wright, R.J., V.C. Baligar, and R.P. Murrmann (ed.). 1991. "Plant-soil interactions at low pH. Developments in plant and soil sciences." Kluwer Acad. Publ., Netherlands.

You can contact Dr. Thomas Rice, in California by fax at 805/756-5412, or by e-mail: trice@calpoly.edu. You can also phone him in San Luis Obispo, CA, at 805(156-2420.

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