COOPERATIVE EXTENSIONNOVEMBER-DECEMBER 2001

VOLUME 21ISSUE 6

INSIDE THIS ISSUE:

Micronutrients 2

Heavy Metals 5

Copper 7

Meet Westfall 8

Arsenic 9

Meet Doesken 10

Zinc Fertilizers 11

Zinc Application 13

Zinc And Dry Beans 14

Phosphorus And Zinc Interaction 15

Iron Chlorosis In Corn 16

Boron 18

Sulfur 19

Web Pages 20

Metals And Micronutrients

Colorado State University, U.S. Department of Agriculture, and Colorado counties cooperat-ing. Cooperative Extension programs are available to all without discriminatin. The informa-tion given herein is supplied with the understanding that no discrimination is intended and noendorsement by Colorado State University Cooperative Extension is implied.

Weighing environmental hazards and economicbenefits

FROM THE GROUND UP

This newsletter focuses on metalsand micronutrients from two points ofview: environmental hazards andagronomic benefits. The newsletterstarts with an introductory article torefresh all of our memories with thebasics. The next several articlesfocus on environmental concerns,specifically, heavy metal contamina-tion of fertilizers, soil copper accu-mulation due to its use in footbathsfor livestock, and arsenic in ground-water. After that, we switch focus toagronomic utilization of micronutri-ents with several articles on zinc thatcover sources, application methods,and interactions with phosphorus.

The last three articles focus on iron incorn, boron in alfalfa and potatoes,and sulfur in wheat. Numerousoutside authors contributed to thisissue including: Terry Tindall fromSimplot, Alan Blaylock from Agrium,Bryan Hopkins from the University ofIdaho, Bart Stevens from the Univer-sity of Wyoming, and Gary Hergertfrom the University of Nebraska. I’mgrateful to all of the contributingauthors and hope this newsletter ishelpful in weighing both the hazardsand benefits of metals and micronutri-ents.

Jessica DavisSoil Specialist

Colorado State University

2 AGRONOMY NEWS

FROM THE GROUND UPagronomy news is a monthlypublication of Cooperative Extension,Department of Soil & Crop Sciences,Colorado State University, Fort Collins,Colorado.

Web Site: http://www.colostate.edu/Depts/SoilCrop/extension/Newsletters/news.html

The information in this newsletter is notcopyrighted and may be distributedfreely. Please give the original authorthe appropriate credit for their work.

Jessica DavisTechnical Editor

Direct questions and comments to:Gloria BlumanhourstPhone: 970 491-6201Fax: 970 491-2758e-mail: gbluman@lamar.colostate.edu

Extension staff members are:Troy Bauder, Water QualityMark Brick, Bean ProductionJoe Brummer, ForagesBetsy Buffington, PesticidePat Byrne, BiotechnologyJessica Davis, SoilsJerry Johnson, Variety TestingRaj Khosla, Precision FarmingSandra McDonald, PesticideJames Self, Soil, Water, & Plant TestingGil Waibel, Colorado Seed GrowersReagan Waskom, Water Resources

Micronutrients In Crop Production

An understanding of micronutrient deficiency symptoms, common conditions lead-ing to deficiencies, and sources of micronutrients is essential to understanding therole of micronutrients in agronomy.

Questions are often raised about therelative importance of micronutrientsin crop production. It has been wellestablished that optimum yieldsgenerally are not possible without N,P and K fertilizers, and the secondarynutrients to a lesser extent. Mostgrowers and dealers follow therecommended rates and methods ofapplication to achieve top yields, butthey may not consider that one ormore micronutrients also may belimiting their yields.

Micronutrients are those elementswhich are essential for plant growth,but are required in much smalleramounts than those of N, P and K.The micronutrients are boron (B),copper (Cu), iron (Fe), manganese(Mn), molybdenum (Mo), zinc (Zn),and chloride (Cl). Because Cl

deficiencies rarely occur, this reportwill discuss the other sixmicronutrients.

Micronutrient deficiencies have beenverified in many soils throughincreased use of soil testing and plantanalyses. Soil tests should beincluded in all micronutrientfertilization programs, first to assessthe level of available micronutrientsand later to determine possibleresidual effects (buildup). Plantanalyses give an indication of themicronutrient status of crops duringthe growing season.

BoronBoron deficiency symptoms firstappear at the growing points. Thisresults in a stunted appearance(rosetting), barren ears due to poor

pollination, hollow stems and fruit(hollow heart), brittle discoloredleaves, and loss of fruits and nuts.

Boron deficiencies are mainly found inacid soils, on sandy soils in regions ofhigh rainfall or under irrigation, andthose soils with low soil organicmatter. Borate ions are mobile in soiland can be leached from the rootzone. Boron deficiencies are morepronounced during drought periodswhen root activity is restricted.Crops that are susceptible to Bdeficiency are alfalfa, sugar beets,clovers, and some vegetable crops.There have been few reported cropresponses to applied B in Colorado.

CopperDeficiency symptoms of Cu aredieback of stems and twigs, yellowing

NOVEMBER-DECEMBER 2001 3

of leaves, stuntedgrowth, and pale greenleaves that wither easily.Cereal crops areespecially susceptible tolow Cu levels, withcurled leaves at tillering,head and stem bending,shriveled grain, anddelayed maturity.

Copper deficiencies aremainly reported onorganic soils (peats andmucks), and on sandysoils which are low inorganic matter. Copperuptake decreases withincreases in soil pH andincreased P and Feavailability in soils.Some crops that aresensitive to Cudeficiency are alfalfa, barley, corn,oats, wheat and some vegetablecrops. Copper deficiencies have notbeen observed in Colorado crops.

IronIron deficiency is expressed as yellowleaves due to low levels of chlorophyll(chlorosis), which first appears on theyounger upper leaves in interveinaltissues. Severe Fe deficiencies maycause leaves to turn completelyyellow or almost white, and thenbrown as leaves die.

Iron deficiencies are found mainly oncalcareous (high pH) soils. Cool, wetweather enhances Fe deficiencies,especially on soils with marginal levelsof available Fe. Poorly aerated orcompacted soils also reduce Feuptake by plants. Uptake of Fedecreases with increased soil pH, andis adversely affected by high levels of

available P, Mn and Zn in soils. Somecrops which are sensitive to Fedeficiency are corn, sorghum, wheatand ornamentals. Iron chlorosis hasbeen widely observed in grainsorghum and on ornamentals inColorado.

ManganeseInterveinal chlorosis on dry beans,and whitish-gray spots on leaves ofcereal crops are Mn-deficiencysymptoms. Brown necrotic spotsappear on leaves with very severe Mndeficiencies, resulting in prematureleaf drop.

Deficiencies of Mn mainly occur onorganic soils, and sandy soils low inorganic matter, and on over-limedsoils. Toxicity of Mn can result insome acidic, high-Mn soils. Cropswhich are susceptible to Mndeficiency are dry beans and some

vegetable crops. There have been noreported Mn deficiencies in Coloradocrops.

MolybdenumMolybdenum deficiency symptoms inlegumes are mainly exhibited as N-deficiency symptoms because of theprimary role of Mo in N

2 fixation.

Deficiency symptoms of Mo in somevegetable crops are irregular leafblade formation (known as whiptail),interveinal mottling and marginalchlorosis of older leaves.Molybdenum deficiencies are foundmainly on acid, sandy soils in humidregions. Plant uptake of Moincreases with increased soil pH,which is opposite that of the othermicronutrients. Crops which aresensitive to Mo deficiency are alfalfa,clovers and some vegetable crops.There have been no reported Modeficiencies in Colorado crops.

4 AGRONOMY NEWS

Oxysulfates are oxides, usuallyindustrial by-products, which havebeen partially acidulated with sulfuricacid, and generally are sold ingranular form. The percentage ofwater-soluble Mn or Zn in oxysulfatesis directly related to the degree ofacidulation. Research results haveshown that at least 35 to 50% of thetotal Zn in granular Zn-oxysulfatesshould be in water-soluble form to beimmediately effective for crops.Similar results would be expected forMn-oxysulfate. Inorganic sourcesusually are the least costly sources perunit of micronutrient, but they may notalways be the most effective forcrops.Synthetic chelates are formed bycombining a chelating agent with ametal through coordinate bonding.Stability of the metal-chelate bondaffects availability of the micronutrientmetals to plants. An effective chelateis one in which the rate of substitutionof the chelated micronutrient for othercations in the soil is quite low, thusmaintaining the applied micronutrientin chelated form.

Relative effectiveness for crops perunit of micronutrient as soil-appliedchelates may be from two to fivetimes greater than that of inorganicsources, but chelate costs may be fiveto 100 times higher. Several chelatesare sold, so relative effectivenessvalues depend on the sources ofchelates and inorganic productscompared.

Organic complexes are made byreacting metallic salts with someorganic by-products of the wood pulpindustry or other related industries.The types of chemical bonding of the

ZincSome zinc deficiency symptoms areshort internodes (rosetting), adecrease in leaf size, chlorotic bandsalong the midribs of corn, mottledleaves of dry beans, narrow yellowleaves in the new growth of citrus,and delayed maturity.

Zinc deficiencies are mainly found onsandy soils low in organic matter andon organic soils. They occur moreoften during cold, wet spring weatherand are related to reduced rootgrowth and activity. Uptake of Zndecreases with increased soil pH, andis adversely affected by high levels ofavailable P and Fe in soils. Somecrops which are susceptible to Zndeficiency are corn, dry beans, lettuceand onions. Zinc application isrecommended for corn grown onColorado soils testing low (<1.5ppm) in available Zn.

Micronutrient sourcesMicronutrient sources varyconsiderably in their physical state,chemical reactivity, cost, andavailability to plants. The mainclasses are inorganic products,synthetic chelates and organiccomplexes.

Inorganic sources include oxides andcarbonates and metallic salts such assulfates, chlorides, and nitrates. Thesulfates are the most common of themetallic salts and are sold incrystalline or granular form. Anammoniated ZnSO

4 solution usually is

applied in polyphosphate starterfertilizers. Oxides of Mn and Zn arealso sometimes used as fine powders,but their immediate effectiveness forcrops is rather low in granular form.

metals to the organic components arenot well understood. While organiccomplexes are less costly per unit ofmicronutrient, they usually are lesseffective than synthetic chelates. Theyalso are more readily decomposed bymicroorganisms in soil. Thesesources are more suitable for foliarsprays and mixing with some fluidfertilizers.

SummaryMicronutrients are as important as theprimary and secondary nutrients inplant nutrition. However, the amountsof micronutrients required foroptimum crop yields are much lower.Soil tests and plant analyses areexcellent diagnostic tools to monitorthe micronutrient status of soils andcrops. Visual deficiency symptoms ofthese nutrients also are wellrecognized in most economic crops.Micronutrient recommendations arebased on soil and plant tissueanalyses, the crop species andexpected yield, management level,and research results.

Because recommended rates usuallyare low, most micronutrients areapplied with NPK fertilizers, but foliarsprays also are frequently applied.Choice of micronutrient sourcedepends on the method ofapplication, compatability with theNPK fertilizer, convenience ofapplication, and the relativeagronomic effectiveness and cost perunit of micronutrient.

John MortvedtFaculty Affiliate

Colorado State University

NOVEMBER-DECEMBER 2001 5

Risk assessments of the use of cadmium, lead, and arsenic in fertilizerfocus on public health and safety.

Heavy Metals In Commercial Fertilizers

Most commercial phosphate,potassium, and micronutrient fertilizersoriginate from natural resources. TheJ.R. Simplot Company, for example,has a modern mining operation on theIdaho/Wyoming border from whichwe extract phosphorus ore. Simplot’smine sits at about 7000 feet inelevation, but was at one time aninland ocean. Sediments associatedwith this body of water had a highconcentration of phosphorus in theform of a mineral called apatite (alsoknown as rock phosphate). Theocean sediments (which are nowrock) also contained smallconcentrations of other elements.Some of these elements providenutrition for growing plants and othershave no nutritional value (such ascadmium, lead, and arsenic). All ofthe elements contained in thephosphorus fertilizer are alsonaturally occurring in the soil towhich the fertilizers are beingapplied.

Public concern over heavymetals in commercial fertilizerhas decreased recently asunderstanding of these elementshas improved. Concern withpublic health, as well asenvironmental degradation, hadsurfaced over the past fewyears. Most of the concern

came about due to popular articlesthat were written to generate interestand public discussion. Much publicdiscussion, thousands of dollarsspent, many hours of deliberation andnew laws initiated have been the finalresults of this information. I guess thequestion to ask is: Are we a betterworld for the time and exposure?Maybe we are.

The fertilizer industry is more closelymonitored and the total amount ofnutrient (especially P) is restricted toagronomic rates (in some areas).Proposed laws in California havemoved closer to accepting Risk-Based Concentrations for the abovementioned elements through theCalifornia Dept. of Food andAgriculture (CDFA). The U.S. EPAhas also conducted an extensive

fertilizer risk assessment to providedirection regarding additionalregulations of commercial fertilizersrelative to non-nutritive elements.They adapted assessments for bio-solids used as a soil amendment andcement kiln dust used as an agricultureliming material. The EPA wasinterested in NPK fertilizers, allmicronutrient fertilizers, and some soilamendments. Nine metals wereevaluated which included arsenic,cadmium, and lead. It is interesting tonote that the EPA did not evaluateRisk-Based Concentrations but askedthree yes or no questions:1) Are commercially available phos-

phate materials safe for humans andthe environment?

2) Are micronutrients safe? and3) Are NPK blended fertilizers safe?

6 AGRONOMY NEWS

Spring 2002Colorado

ChemsweepColorado

Waste Agricultural PesticideCollection Program

Registration due by February 20, 2002.Call 1-888-242-4362 for more information.

To answer these questions, the EPAevaluated exposure routes using farmfamilies (adults and children) as theirreceptors. The exposure routes wereas follows:

�Direct ingestion of fertilizer prod-ucts during application

Incidental consumption of soil Inhalation of particles or fertilizer

vapors during application Ingestion of plant and animal

products produced on fertilized soil Ingestion of fish from streamsadjacent to fertilized fields

The EPA evaluated hundreds ofcommercially available products andfound only four materials that hadelevated levels of metals above anaccepted standard of concern. Thematerials of concern included oneliming material, and one each of iron,boron, and zinc micronutrientfertilizers. The standard of concernwas not a cancer risk, but listed as ahazard index. The hazard indexseparates products that are “safe”

from those that need furtherevaluation.

Two additional risk assessments havealso been conducted evaluating heavymetals contained in fertilizers. Onewas conducted for The FertilizerInstitute and the other by theCalifornia Department of Food andAgriculture (CDFA). Both of thestudies had primary concern forpublic health and safety in associationwith exposure to fertilizer materials.The CDFA study not only looked atexposure to humans from handling oringesting the fertilizer, but alsoevaluated heavy metal uptake invegetable crops, root crops andgrains. The CDFA study has resultedin a new regulation restricting levels ofarsenic, cadmium, and lead inphosphate and micronutrientfertilizers. The new regulation will beimplemented in California in 2002.

A more interesting study (from anagronomic viewpoint) is currentlybeing conducted by Washington StateUniversity under the direction of Drs.

Bob Stevens and Shiou Kuo andother researchers in Washington.Their study included the application ofboth raw rock phosphate, treblesuper phosphate (0-45-0) from twosources, and a zinc micronutrientfertilizer. These fertilizer materialswere applied at both agronomic ratesand as much as eight times agronomicrates to field plots, which wereplanted to wheat or potatoes. Theprimary goal was to determine howfertilizer-loading rates would impactcadmium and lead levels of these twocrops. At the end of the 2000 growingseason there were no effects on yield.

Cadmium and lead concentrationsincreased in both the soil and thepotato tuber and wheat grain relativeto increased application rates.However, even at the high rate (8 xagronomic rate), the tissueconcentration was far below any ofthe Risk-Based Concentrationsestablished by EPA or CDFA. Themost interesting results from theirwork were relative to the use of rawrock phosphate. This materialsurprisingly decreased grain yield inthe first year of the study. Unless rawrock P is treated with sulfuric acid andprocessed into 0-45-0 it is difficult forcrop P demands to be met.

Results of several risk assessments, aswell as the above field study andother published research, have shownthat commercial fertilizers are safewhen used at agronomic rates.

Terry TindallManager of Agronomy

J.R. Simplot Co.

NOVEMBER-DECEMBER 2001 7

Is Copper In Dairy Footbaths A ProblemFor Crops And Cows?Copper sulfate used in dairy footbaths can lead to soil copper buildup.

Most dairies in Colorado use coppersulfate in foot baths to control hoofinfections. After use, the foot bathsare usually channeled into thewastewater lagoons along with therunoff water and flush water from themilking parlors. Then, the lagooneffluent is usually applied to foragecrops being grown to feed the cows.

An article in Hoard’s Dairyman byE.D. Thomas in July 2001 broughtthis issue to the forefront with specialconcern for copper accumulation inforage crops and subsequent toxicityto dairy cows.

RegulationsAt this time, there are no regulationsthat pertain to copper applications tocrops in the form of dairy effluent.However, both the biosolids and hogregulations require regular soilsampling and analysis for copper. Inaddition, The Colorado Departmentof Health and Environment limits theannual and cumulative application ofmetals in biosolids, including copper.The annual limit for copperapplication in this form is 67 lbs/acre,and the cumulative or lifetime loadinglimit is 1340 lbs copper per acre.Officially, these limitations do notapply to dairies, unless they usebiosolids. However, the wise milkproducer will pay attention to theseregulations as possible precedents fordairy regulation in the future.

Copper quantitiesWe calculated typical copper usageby Colorado dairies and found arange from about 1000 lbs Cu/yearup to over 10,000 lbs Cu/year. Thiscalculation is based on the followinginformation: 5-10 lbs copper sulfate isdissolved in 25 gallons of water,copper sulfate is 25% copper,footbaths hold 25-75 gallons of waterand are changed about nine times perday and used two to three times perweek. So is 1000-10,000 lbs Cu/yra problem? Obviously, the answerwill depend on how much acreage theeffluent is spread on. If the effluent isall applied through one center pivotonto 125 acres, this is equivalent to 9to 84 lbs Cu/yr. The high end of therange is over the biosolids annual

loading limit, so these values are highenough to warrant furtherconsideration.

Toxicity to bacteria in lagoonsThe first potential hazard of thecopper could be to bacteria in thewastewater lagoons. Some coppermay re-precipitate or settle out intothe lagoon sludge, thus reducing thecopper levels in the effluent itself.However, effluent copper levels maystill be toxic to bacteria, and this isimportant because most lagoons aresites for either aerobic or anaerobictreatment of waste by bacteria. Onelarge Colorado dairy recently haddifficulty with low bacterialpopulations and determined that this

8 AGRONOMY NEWS

was probably due to the coppersulfate footbaths.

Toxicity to cropsWhen copper is applied to our soils, itis strongly bound to clay minerals.Exchangeable copper is held muchmore tightly than other cations, and isnot readily available to plants.Organic matter also binds copper, sothe more organic matter and clay thata soil has, the greater the potential forcopper adsorption will be. Inaddition, increasing soil pH reducescopper availability to plants, allowinggreater soil copper accumulationwithout subsequent plant toxicity inour high pH soils. Because of itsstrong binding, copper leaches verylittle, and accumulates in the soilsurface.

Copper is not readily mobile in plants,resulting in higher copper levels inroots than in shoots. Therefore,copper toxicity often results indecreased root growth and damageto root cell membranes. Researchershave found that high levels of calciumcan alleviate copper’s toxic effects onmembranes, which is fortunate forColoradoans who generally have highsoil calcium levels. Copper toxicitymay also induce iron deficiencies orgeneral chlorosis in plants.

There is tremendous variability inplants’ ability to tolerate high copperlevels. In general, a level of 20-30parts per million (ppm) in the leavesmay be considered toxic, but this is abroad generality across all plantspecies and should not be applied tospecific crops without additionalinformation. Some researchers have

meetDwayne Westfall

Dwayne Westfall is a Professorin the Department of Soil andCrop Sciences. His researchareas include soil fertility man-agement, dryland croppingsystems management and preci-sion agriculture. He also teaches“Soil Fertility Management” anda course for graduate students“Presentation of ScientificInformation”. Dwayne grew upon a potato and small grain farmin Idaho. He received his B.S.degree from the University ofIdaho and Ph.D. from Washing-ton State University. He has held

positions at Texas A&M University,Great Western Sugar Company andworked for two years in Pakistanon CSU’s On-Farm Water Man-agement Project. His favoritepastime is spoiling his 10 grandchil-dren and then turning them over totheir parents!

noted that legumes, such as alfalfa,are more sensitive to copper toxicitythan grasses, so care should be takenwhen growing alfalfa on soils thatreceive Cu-enriched effluent.

Toxicity to livestockThe maximum tolerable level ofcopper in diets of lactating dairy cowsis 100 ppm, while the minimum is 10ppm. Therefore, when copper sulfateis being used in footbaths and thewaste is channeled to the lagoon andapplied to land, producers shouldhave copper analyzed in their foragesbefore feeding them, as part of theirnormal forage testing program. Beaware that other types of livestockhave different critical levels; forexample, 20 ppm copper can be toxicto sheep.

Actions to consider Calculate your copper use and land

application rate. Consider alternatives to copper

sulfate (tetracycline or moresoluble coppers that allowlower copper use rates).

Divert the footbath water, so it doesnot enter the lagoons.

Analyze the copper content offorage grown on land thatreceives effluent with copperin it. Monitor forage copperlevels annually to see if theyare increasing.

Increase the acreage of cropsreceiving the lagoon effluent,in order to dilute the copperover more area.

Jessica Davis and Bill WailesExtension Soils and Dairy Specialists

Colorado State University

Is There ArsenicIn Your Drinking Water?

Hot spots of arsenic exist in groundwater on the West Slope, San Luis Valley,and northeastern Colorado.

Shortly after President George W.Bush took office, he suspended oneof the last acts of the Clintonadministration, a tightening of thefederal standard for arsenic levels indrinking water. President Clinton hadlowered the federal standard from 50parts per billion (ppb) down to 10ppb. In March, the EPA asked for astudy which the National Academy ofSciences (NAS) completed inSeptember. This study concludedthat an arsenic standard of 10 ppb stillresults in a cancer risk (1 in 500) thatfar exceeds what EPA usuallyconsiders acceptable (1 in 10,000).These cancer risks are based onconsuming 2 liters (about eight 8 ozglasses) of this contaminated watersource per day over a lifetime.Arsenic in drinking water is known tocause bladder, lung, and skin cancers.On October 31, the Bushadministration announced that it isadopting the 10 ppb standard, basedupon the NAS study. However,some people argue that the NASstudy supports the need for an evenlower standard of 3 ppb in drinkingwater (a 1 in 1,667 cancer risk).

Where does it come from?Arsenic is a naturally occurringelement in rocks, soils, and water incontact with them. Widespread high

concentrations of arsenic ingroundwater are generally attributedto natural sources, such as dissolutionof rocks and minerals. However,arsenic is used in many industrialproducts. About 90% of industrialarsenic is used as a pesticide in woodpreservation. Arsenic is also used inmining, smelting, and some agriculturaluses, specifically, growth promotion inswine and poultry. These uses couldalso lead to pollution of groundwater.

Colorado levelsThe U.S. Geological Survey hascollected and analyzed arsenic innearly 20,000 wells across the U.S.(reported by Sarah J. Ryker in theNovember 2001 issue of Geotimes).In general, they found that the highestgroundwater arsenic levels are in thewestern U.S. Specifically, inColorado there are a few hot spotson the West Slope where arseniclevels in groundwater exceed 50 ppb

(the old standard). In addition, thereare a few locations in northeasternColorado and the San Luis Valleywhere groundwater arsenic levelsexceed 10 ppb (the new standard).

In Colorado, only 18% of people relyon groundwater for drinking water.Most of these people are locatedlargely in the Eastern plains, but anincreasing number of foothills andmountain homes rely on groundwater.Nineteen of Colorado’s 63 countiesrely almost exclusively ongroundwater for a drinking watersource.

The U.S. Geological Surveydeveloped county maps that showcounty-by-county arsenic distribution.Twenty-five percent of well samplesfrom Logan, Sedgwick, andSaguache counties had arsenicconcentrations of at least 5 ppb.Phillips, Alamosa, Rio Grande, RioBlanca, and Garfield had 25% ofsamples that exceeded 3 ppb.

Community implicationsWater systems across the country willhave to be in compliance with the 10ppb standard by 2006. Almost 97%of the affected water systems servefewer than 10,000 people each.Therefore, many small communities

NOVEMBER-DECEMBER 2001 9

will be affected by the new standard.These communities will be forced toeither upgrade their water filtrationsystems or find alternative watersupplies. This changes are likely toincrease water costs for consumers,while reducing their cancer risk.

Homeowners with private wells arenot regulated under water qualitystandards. However, homeownerswho have excessive arsenic levels intheir water and do not filter theirwater or find another water source,will potentially be putting their healthat risk.

Actions to considerIf you get water from a public watersystem, ask for the results of theirarsenic analysis. If you drink from aprivate well, take a water sample andhave it analyzed. You can then decidewhether to purchase a home filtrationsystem to remove arsenic from yourdrinking water.

Jessica Davis and Troy BauderExtension Soil and Water Quality Specialists

Colorado State University

10 AGRONOMY NEWS

meetKathy Corwin Doesken

Kathy Corwin Doesken is thenew research associate forJessica Davis. Kathy startedOctober 15th, just in time tohelp with fall field work. Sheis a graduate of ColoradoState University, Departmentof Soil and Crop Sciences,and is pleased to return towork in the department,where some folks rememberher. She is interested in soilfertility and nutrient resourcemanagement. Kathy hasexperience teaching and islooking forward to bringingtogether her interests in educa-tion and agriculture as Davis’research assistant.

She is married to Nolan, who isalso employed by CSU in theDepartment of AtmosphericScience. Kathy, Nolan, andtheir two teen-aged children,Gail and Joel, live northwest of

ArsenicContinued from page 9

For other issues of the Agronomy News on agricultural topics like:

Biotechnology Dry Bean Production Variety Trial ResultsNitrogen Fertilizer Precision Agriculture Salinity

Phosphorus and Runoff

Visit our web site:

http://www.colostate.edu/Depts/SoilCrop/extension/Newsletters/news.html

town on an old farm. Kathy has beeninvolved in small-scale farming, raisinghorses, and making lots of compost.

Kathy fills the position vacated byKirk Iversen, who left CSU in Augustto take a position at Auburn Univer-sity.

Zinc Fertilizers, Is There A Difference?

Plant availability of zinc depends on water solubility of fertilizers.

Zinc (Zn) is one of the micronutrientsrequired for plant growth and themost common micronutrient that isdeficient in Colorado soils. One ofthe main reasons for this is that oursoils are generally alkaline in pH andcontain free lime (CaCO

3), which ties

up the Zn in unavailable forms. TheZn sensitive crops grown in Coloradoinclude corn, sorghum, sudan,sorghum X sudan hybrids, dry beansand potatoes. These crops respondto Zn fertilization if the soil Zn levelsare low. The next logical question is“are my soils low in available Zn?” -only a soil test can tell you this. Allsoil testing laboratories operating inthis region can perform this test foryou. So, I get a soil test performed,and sure enough, the soil tests low inZn! What’s next? Well, theapplication of a Zn fertilizer of course.The question we would like toaddress is “are all Zn fertilizers equallyeffective in correcting Zndeficiencies?”. In the market place,disagreement exists regarding theeffectiveness of the many Zn fertilizersthat are being sold.

Some people question the importanceof water solubility of a granular Znfertilizer and its relationship to Znavailability to plants. What is watersolubility and why should it matter?Water solubility indicates how muchof the fertilizer will dissolve in water.Why does it matter? Most nutrientsare taken up from the soil solution bythe plant; therefore, if a fertilizer will

not dissolve in the soil solution, it willprobably not be an effective fertilizer.

Solubility is related to the processused in fertilizer manufacturing and theprimary product used as a Zn source.Many Zn fertilizers in the marketplace are manufactured from industrialby-products such as zinc oxide(ZnO). Unfortunately, ZnO is notwater soluble and not an effective Znfertilizer on our alkaline soils. Toprepare granular Zn fertilizer fromZnO, it is reacted with sulfuric acid(H

2SO

4) to improve solubility and

promote granulation. The finalproduct will be a mixture of ZnO, andzinc sulfate (ZnSO

4). Zinc sulfate is

essentially 100% water soluble and agood Zn source for plants. The moreacid that ZnO is reacted with, themore ZnSO

4 that is formed, and the

higher the water solubility of the finalfertilizer material. Fertilizers that aremixtures of ZnO and ZnSO

4 are

called Zn oxysulfates.

We conducted some studies todetermine if the percent watersolubility of a granular Zn fertilizer is ameasure of its ability to supply Zn tothe plant. Corn plants were grown inthe greenhouse on a Zn-deficient soil.Six Zn fertilizer materials wereevaluated ranging from 99.9% to0.7% water solubility. The fertilizersincluded ZnSO

4 and five Zn

oxysulfate fertilizers ranging in watersolubility from 98.3 to 0.7% watersolubility: Zn20 (98.3%), Zn27

(66.4%), Zn40 (26.5%), ZnOxS(11%), and ZnOS (0.7%). The firstnumber is the total Zn content of thefertilizer and the number in parenthesisis the water solubility. The ZnSO

4

contains 36% Zn and is about 100%water soluble. We use ZnSO

4 as our

reference to which we compare allother fertilizers. Fertilizer rates usedwere equivalent to 0 (control), 5, 10and 20 lb Zn/A. Plants wereharvested about 6 weeks afteremergence. Previous work hasshown that there is no need to growcorn plants to maturity to evaluate theeffectiveness of different fertilizersources, as results will be similar tothose during early growth stages.Plant growth (dry matter production)and Zn uptake were measured. Weonly present the plant growth datahere.

Zinc-deficiency symptoms wereobserved on the corn plants grownwith the two fertilizers with the lowestwater solubility, ZnOxS (11%) andZnOS (0.7%). These symptomswere evident as early as 5 days afteremergence. Pronounced bands ofchlorosis appeared on the leaves,starting near the leaf whorl andextending up the leaf. These bandsturned white with time. As plantgrowth progressed, Zn-deficiencysymptoms also occurred with theZn40 (26.5%). Plants fertilized withthese three materials were stunted ingrowth. Slight Zn deficiencies werealso observed with Zn27 (66.4%),

NOVEMBER-DECEMBER 2001 11

14

16

18

20

22

24

26

28

30

0 5 10 15 20 25

Zn applied (lb/A)

Dry

mat

ter

(g/p

ot)

ZnSO4

Zn20

Zn27

Zn40

ZnOxS

ZnOS

Figure 1. Corn dry matter production as affected by Zn fertilizerapplication rates and sources.Figure 1. Corn dry matter production as affected by Zn fertilizerapplication rates and sources.

but the reduction in plant growthwas very small.

The dry matter production for thevarious Zn fertilizers is shown inFigure 1. Based on the plantgrowth response, three groups ofZn fertilizer materials wereidentified: (i) ZnOS (0.7%)resulted in no significant growthincrease with Zn application (Fig.1), (ii) Zn40 (26.5%) and ZnOxS(11%) resulted in a small increasein corn growth as Zn rateincreased and (iii)

ZnSO

4 (99.9%),

Zn20 (98.3%), and Zn27 (66.4%)all increased growth substantially.The very low agronomiceffectiveness of ZnOS (0.7%),ZnOxS (11%), and Zn40 (26.5%)is related to their lower watersolubilities and the inability of thesefertilizers to release Zn to theplant. The application of highrates of Zn from fertilizerscontaining low water soluble Zndid not satisfy the plant’s needs.

A Zn application rate of 5 lb/Awas sufficient to maximize drymatter production when Zn wasapplied as Zn20 (98.3%), Zn27(66.4%), and ZnSO

4 (99.9%). In

fact, no significant differenceswere observed between 5 ascompared to 10 and 20 lb Zn/A.In contrast, Zn40 (26.5%)required 20 lb/A to obtainoptimum dry matter production(Fig. 1). This clearly shows thatwater solubility of granular Znfertilizer was related to availability.

ConclusionsThe agronomic effectiveness of thesix granular Zn fertilizers studieddecreased as the percent water-

soluble Zn decreased: ZnSO4 (99.9%) >

Zn20 (98.3%) > Zn27 (66.4%) > Zn40(26.5%) > ZnOxS (11%) >ZnOS(0.7%). High correlations were foundbetween water solubility of Zn in thefertilizer material and plant response. Weconclude that granular Zn fertilizersshould have water-soluble Zn levels of atleast 50% to be effective in supplyingadequate Zn levels for the current crop.Knowing the total Zn content of afertilizer is not enough to determine whichfertilizer you should use. You need toknow the degree of water solubility ofgranular Zn fertilizers before youpurchase them. Ask your fertilizer dealerfor this information and if the watersolubility is not at least 50%, use adifferent material that satisfies thisrequirement.

Do these greenhouse results apply tofield conditions?Many people ask this question. Undersome circumstances the answer is NO.However, when a greenhouse study is

used to evaluate the availability ofmicronutrients to plants the results aredirectly applicable to field conditions.In fact, many researchers havereported that “if a micronutrientdoesn’t do the job in the greenhouse,it won’t work in the field”. Thereason is that in a greenhouse studyplant roots are confined to a smallvolume as contrasted to a very largerooting volume that occurs in the field.This results in a much higher densityof roots in the soil in the greenhouseand a greater chance for the plant’sroots to come in contact with thefertilizer granule, or its diffusion zone.Consequently, this is an advantage tofertilizers that have a low watersolubility. SO, if a fertilizer doesn’twork in the greenhouse, it won’twork under field conditions!

Dwayne Westfall and Bill Gangloff

Professor and Research AssociateColorado State University

12 AGRONOMY NEWS

Zinc Application Methods

Band or starter applications of zinc are best.

The primary methods of applying zinc(Zn) fertilizer to beans are broadcast,banding, and foliar sprays. Eachmethod has advantages anddisadvantages. A Zn fertilizer can beblended into other fertilizers beingbroadcast. While this is rapid andconvenient, broadcasting zinc has notproduced consistent responses, evenon low-testing soils. Many Coloradosoils have high Zn-fixing capacity. Inother words, much of the zinc appliedreacts with other soil minerals andbecomes unavailable to plants.Availability is reduced further if soilconditions, such as compaction,restrict root growth.

Banding concentrates Zn in the rootzone, improves the probability of rootcontact, and reduces fixation.Greater efficiency of bandapplications means that lower ratescan be used to get the same cropresponse. Broadcast applicationsusually call for 5-10 lbs Zn/acre while1-5 lbs Zn/acre is adequate forbanded application. Research studiescomparing band and broadcastapplications of Zn have demonstratedmore consistent responses to bandingthan to broadcasting. In some cases,banding has produced crop responseseven on high-Zn soils.

Foliar applications are usually used tocorrect an unanticipated deficiencythat occurs during the growingseason. A water-soluble fertilizersuch as a Zn chelate or Zn sulfate isdissolved in water and applied atabout 0.5 to 1.0 lbs Zn/acre inenough water to wet foliage, about20-30 gal of solution per acre.Repeated applications are oftennecessary to maintain healthy plantswhen soils are deficient in availableZn.

A discussion of Zn application on drybeans should include the use of starterfertilizers. Starter fertilizers have beenshown to improve early growth anddevelopment of many crops. InColorado, dry beans are oftenplanted into cold, high-pH, loworganic matter soils. Compaction isoften present. Under theseconditions, early plant growth anddevelopment are slow and manynutrients, especially Zn, are lessavailable.

Yield potential of beans is establishedduring early vegetative growth.Flower cells are being formed at thistime. Stress during this formativeperiod reduces the number of flowercells that are formed and thereby

reduces yield potential. By applyingZn in a starter fertilizer, earlyvegetative growth is increased, thephotosynthetic factory is greater, andyield potential increases.

While starters are not commonly usedon beans, Wyoming research hasdemonstrated significant profitopportunities with the use of starters.As little as 1 lb Zn/acre in a startercontaining N and P was effective inproducing an additional 130 lbs beanyield/acre, hastening maturity by twodays, and increasing profit by morethan $20/acre over a startercontaining only N and P. Thisresponse was observed on soils withvery high soil Zn. Be aware thatstarters should not be placed in directcontact with bean seed. Beans arevery sensitive to salts, and stand losswill result from seed-placed fertilizer.

Band or starter application of Zn onbeans in Colorado is highlyrecommended if soil pH is high, Nand/or P supply is high, soilcompaction is present, or yieldpotential is high. The advantagesoutweigh the inconvenience.

Alan BlaylockSenior Agronomist

Agrium U.S. Inc.

NOVEMBER-DECEMBER 2001 13

Dry Bean Response To ZincFoliar application on irrigated dry beans in southwestern Colorado increasedyield in one out of two years.

Dry bean is an important crop inColorado. It ranks fifth in acreageand total value in Colorado and fourthin the U.S. in production. Insouthwestern Colorado, dry bean isproduced mostly under drylandconditions but much higher yields canbe achieved with supplementalirrigation. Most agricultural soils insouthwestern Colorado haverelatively high pH (7.0 to 8.0) and arelow in organic matter and available P.High pH and low organic matter areamong the factors that favor thedevelopment of Zn deficiency. Zincdeficiency causes chlorosis in beanplants and can delay maturity andreduce seed yield.

Khan and Soltanpour (Khan, A., andP.N. Soltanpour. 1978. Factorsassociated with Zn chlorosis indryland beans. Agron. J. 70: 1022-1026) attributed chlorosis in drylanddry bean in southwestern Colorado tohigh soil P/Zn ratio and a highincidence of root rot disease. Thechlorotic bean plants were situatedlower on the slope than the greenplants, which led the authors tospeculate that the higher soilmoisture in lower areasmay have increased Pavailability. Soil Zn levelwas about the same, 0.5ppm in the areas withgreen or chlorotic beanplants. Spraying thechlorotic plants with a

1% Zn solution removed chlorosisand increased bean yield by 18 to92%, but not up to the yield level ofthe healthy plants. The difference inyield between the green plants andthose sprayed with Zn was attributedto the higher incidence of root rot inthe chlorotic plants. Root rot resistantpinto bean varieties have beenreleased since 1981 and are nowwidely grown in southwesternColorado.

A field experiment was initiated in1999 to determine the effect of Znapplication rate and method onirrigated pinto bean yield insouthwestern Colorado. ‘Bill Z’pinto bean was planted in early Juneat approximately 22 seeds m-2 in1999 and 2000 at the SouthwesternColorado Research Center at YellowJacket, CO. A second variety,‘Poncho’ was included in the 2000experiment. The soil type wasWetherill silty clay loam. Zinc sulfatewas broadcast shortly before plantingbeans in both years at 5 and 10 lbsZn/acre and incorporated into the soilwith a field cultivator. Foliar spray of

a 7% zinc sulfate solution was madeat the same rates with a 3-m boomsprayer four to five weeks afterplanting.

Bean seed yield was much higher in2000 (2936 lbs/acre) than in 1999(2120 lbs/acre), probably due tobetter irrigation water management in2000. No symptoms of zincdeficiency were visible before or afterthe foliar spray in any of thetreatments in 1999 or 2000.However, a foliar application of 5 lbsZn/acre resulted in significantly higherBill Z seed yield in 1999 compared tothe control (over 500 lbs/acre more).The broadcast treatments had noyield effect in 1999. Zinc applicationrate or method did not affect Bill Z orPoncho seed yield in 2000. Futurestudies will include shallower soilsampling and a close look at soilspatial variability since chlorosis oftenoccurs in patches in bean fields insouthwestern Colorado.

Abdel BerradaResearch Scientist

Southwestern Colorado Research CenterJessica Davis

Extension Soil SpecialistColorado State University

14 AGRONOMY NEWS

Soil Zn (ppm)pH OM AB-DTPA Mehlich-3

1999 7.2 1.0 % 0.3 312000 7.5 1.1 % 0.6 20

Table 1. Soil test results

Banding high rates of P can induce Zn deficiency in high pH soil.

Phosphorus And Zinc Interaction

Phosphorus and zinc are essentialnutrients for plant growth. Unfortu-nately, these nutrients can act an-tagonistically with one another incertain circumstances. This antago-nistic reaction is know to cause yieldreductions in many crops.

Yield reductions due to this interactionare caused by either phosphorus orzinc deficiencies. Deficiencies typi-cally occur when a nutrient is presentin short supply. In this case, thenutrient is present in marginal tonormal levels, but the antagonizingnutrient is present in such a largequantity that it forces a deficiency ofthe other. In other words, excessivephosphorus can cause zinc to becomedeficient in plant tissue. Similarly,excessive zinc can cause phosphorusdeficiency, however, this phenomenonis very rare.

The mechanism of this phosphorus-zinc interaction occurs primarily in theplant root, rather than in the soil, asmany people suppose. Excessiveconcentrations of phosphorus in theplant root tesult in the binding of zincwithin root cells. The zinc becomespart of the “fabric” of the root and,therefore, becomes unavailable fortransport to leafves, where it isneeded for normal plant growth.

Phosphorus-induced zinc deficienciesare more common than zin-inducedphosphorus deficiencies. This isbecause it is much more common forgrowers to apply substantial amounts

L o c a tio n S o il B o ro n(p p m )

S o il O rg a n ic M a tte r(% )

S o il T e x tu re

Y e llo w J a c k e t 0 .4 1 .1 s ilty c la y lo a m

H o ly o k e 0 .2 1 .2 s a n d y lo a m

C e n te r 0 .1 1 .0 g ra v e lly s a n d y lo a m

NOVEMBER-DECEMBER 2001 15

of phosphorus fertilizer as comparedto zinc fertilizer.

Zinc deficiency caused by excessivephosphorus can occur if:

Zinc concentrations in the soil arelow, especially in high pHand/or calcareous (excesslime) soil, and

High rates of phosphorus fertilizerare applied.

A phosphorus-induced zinc deficiencyis uncommon in soils that simply havea high soil-test phosphorus level. Infact, these deficiencies occur just asreadily in soils with low soil-testphosphorus levels. In other words,this phenomenon is more related tothe amount of fertilizer applied for thecurrent season rather than the levelalready present in the soil.

The method of phosphorus fertilizerapplication also impacts the likelihoodof inducing a zinc deficiency. Con-centrated bands of phosphorusfertilizer tend to induce zinc deficien-cies more commonly than broadcastapplications. The probability ofcreating a zinc deficiency increases asthe rate of phosphorus in the bandincreases.

Producers applying substantial

amounts of manure often ask if thevery high levels of phosphorus in themanure could induce a siznc defi-ciency. Although it is true that manurecontains a large amount of phospho-rus, it also contains organically-complexed zinc, which helps toprevent the deficiencies from occur-ring.

The manure effect and research onthis interaction demonstrate how toprevent phosphorus induced zincdeficiencies:

Base phosphorus fertilizer rates onprudent soil-testrecommendations.

Apply a moderate amount of zinc ifchoosing to apply excessiverates phosphorus fertilizer,especially when band applied.

Include a small amount of zinc(<1.5 lb/acre) in phosphorus-based starter mixes,especially if the zincconcentration is low ormarginal based on soil-testdata.

Do not apply zinc fertilzier if soil-test zinc level is abovemarginal levels and allphosphorus is being appliedvia broadcast methods.

Bryan HopkinsPotato Cropping Systems Scientist

University of Idaho

Managing Iron Chlorosis In Corn

Ferrous sulfate in the seedrow increased yield of susceptible and toleranthybrids.

Some soils of the western plains andinter-mountain west have chemicaland physical characteristics that causeiron deficiency in corn. Affected cornplants typically are stunted and haveyellow (chlorotic) leaves with veinsthat remain somewhat green, resultingin a striped appearance. The severityof the symptoms varies from year toyear depending on the weather;symptoms usually are worse in cooland wet conditions. Mild yellowingmay disappear when the weatherturns warmer and drier, but moderateto severe yield reductions are usuallythe result when chlorosis persists forthe entire growing season.

We don’t know exactly why certainsoils cause iron chlorosis to develop,while other soils with similarcharacteristics produce healthy corn.Soil tests for iron (DTPA or AB-DTPA) do not always show low Felevels, which complicates predictionof the problem. Affected soils dotypically have high pH (7.8 or higher)and contain free lime (calciumcarbonate). High sodium, poordrainage, low organic matter and highphosphorus have also beenimplicated. In some cases theproblem lies in the subsoil (16-24inches deep) rather than in the plowlayer. Whatever the cause, iron

Fertilizer Source Application RateHybrid

Susceptible Tolerant(lbs FeSO4•7H2O per acre) —— grain yield, bushels per acre

Check 24 C 122 Bliquid 50-75 117 B 156 Adry FeSO4•7H2O 50 133 AB 157 Adry FeSO4•7H2O 100 146 A 169 Adry FeSO4•7H2O 150 143 A 157 A

availability (not necessarily iron levelsper se) in these soils is very low. As aresult, it is usually ineffective to try tocorrect the problem by broadcastingiron fertilizers. Applying soilamendments to modify soil pH isusually not an economical option,either.

The most commonly recommendedapproach is the use of chlorosis-tolerant corn hybrids. Genetictolerance levels vary greatly fromhybrid to hybrid, and most seedcompanies can provide information oneach hybrid’s level of resistance. Inmany cases, use of tolerant hybrids

A, B, C Treatments with a common letter are not significantly differentwithin hybrid type (p<0.05).

Table 2. Results from Nebraska small plot study showing effects ofseed-row applied iron fertilizer on corn yield (average of 3 years).

16 AGRONOMY NEWS

will provide an acceptable level ofcorrection, but yield-limiting chlorosiswill still develop in the most severesoils. In these cases, either foliar orseed-row applications of iron may bebeneficial.

A commonly recommended approachfor foliar application is to apply a 1%solution of ferrous sulfateheptahydrate (FeSO

4•7H

2O) every 7

to 10 days beginning when chlorosisfirst becomes evident and endingwhen emerging leaves are no longerchlorotic. Iron chelates are alsowater soluble and produce similarresults to the ferrous sulfate withoutthe risk of burning the leaves, butchelates are considerably moreexpensive than ferrous sulfate. Whenthese guidelines are followed, foliarapplications are usually effective, buteconomical yield increases may notoccur if applications are made too lateor if they are not repeated at therecommended intervals.

Recent research at the University ofNebraska West Central Research andExtension Center was conducted toevaluate a second option for applyingiron. In this study, iron fertilizerplaced in the seed row consistentlyincreased corn yield compared to anuntreated check. Banding thefertilizer protects it from being tied upby the soil, and the seed-rowplacement enables the small roots ofthe corn seedling to access the ironearly in the growing season. Dry

ferrous sulfate applied at a rate of 50to 100 pounds per acre (at a cost of$8.50 to $17.00 per acre) was themost effective treatment evaluated,but chelated iron (FeEDDHA at 2.5to 4 pounds per acre) and a lowersolubility iron sesquioxide (fromAgrium U.S. Inc. applied at a rate of200 pounds per acre) also producedsmaller, but significant yield increases.Seed-row applied iron fertilizerproduced substantial yield increaseswith both chlorosis-susceptible andchlorosis-tolerant corn hybrids (Table1). The yield benefit varied from yearto year as the weather influencedchlorosis severity, but a positiveresponse was observed in every year.

Some producers and agronomistsmay be hesitant to place fertilizermaterials in direct contact with theseed at these relatively highapplication rates because of the riskof salt damage to emerging seedlings.This concern appears to beunwarranted as the Nebraska resultsshowed no evidence of standreduction, except in 2 of 5 yearswhen ferrous sulfate was applied at arate of 150 pounds per acre. Nostand reduction was observed atapplication rates of 100 pounds peracre or less.

While the dry iron materials are veryeffective, many producers feel theyare less convenient than liquids.Chelated iron can be dissolved inwater and applied as a liquid, but this

is probably not economical due to thehigh cost of chelates. A liquidformulation of ferrous sulfate is notcurrently available commercially, andbecause the solubility of ferrous sulfatelimits the concentration of a liquidformulation to 5% iron, a suitablecommercial product may not beforthcoming. A 5% iron solution,made by dissolving ferrous sulfate inwater, was evaluated in the Nebraskaresearch. While it was effective inboth small and large plot trials, itsperformance did not equal that of thedry ferrous sulfate, probably becausethe low solubility limited the totalamount of iron that could be appliedper acre.

Chlorosis development is usuallyspotty and, while the severity ofchlorosis varies from year to year, thelocation of these areas within a fieldusually remains consistent. Thus, themost economical approach tomanaging iron deficiency chlorosis inthese fields may be to apply fertilizermaterials only to those areas in thefield where chlorosis is a consistentproblem. Research is now beingconducted to evaluate this site-specificapproach on a production scale.

Bart StevensExtension Soils Specialist

University of Wyoming, Powell Research andExtension Center

Powell, WY

Gary HergertDirector

West Central Research and Extension CenterUniversity of Nebraska

North Platte, NE

NOVEMBER-DECEMBER 2001 17

Boron Fertilization Of Potatoes And AlfalfaEven on sandy soils with low B levels, no yield or quality responseswere found.

Boron is an essential plant nutrient forall crops. It plays important roles incell wall synthesis, sugar transport,and seed production. Alfalfa isconsidered to be a crop with a high Brequirement, while potatoes requirelower B levels.

Boron deficiencies are found mostoften in sandy soils, with low organicmatter contents, and high soil pHlevels. Deficiency symptoms in alfalfaare described as “yellow-top.” Theyounger leaves turn yellow or redbetween the veins, rosetting developsdue to shortened stems, and, ulti-mately, the terminal bud dies. Inpotatoes, symptoms include discol-oration and death of the terminalbuds, stubby roots, short internodes,and bud and flower drop.

We initiated several studies from1997-1999 to evaluate the impact ofB application on irrigated alfalfa yieldand on yield and quality of two potatocultivars. We sought out soils withlow B levels, low organic matterlevels, and coarse textures and settledon three locations: one in southwest-ern Colorado near Yellow Jacket(alfalfa), one in northeastern Coloradoin the sandhills near Holyoke (alfalfa),and one gravelly soil in the San LuisValley near Center (potatoes). Eachstudy site was evaluated for twoyears. Soil properties are givenbelow.

The alfalfa varieties were Pioneer5454 at Holyoke and Archer atYellow Jacket. Two potato cultivarswere evaluated: Russet Norkotah andRusset Nugget. SoluborTM wasapplied pre-plant to potatoes at 0, 1,and 2 lbs B/acre. Foliar applicationof SoluborTM was made to alfalfa inApril at rates of 0, 0.5, 1, 2, and 4 lbsB/acre.

There was no significant impact of Bfertilizer application on alfalfa yield forany of the cuttings in any of the foursite-years. There was also nosignificant impact on potato yield(total or components), specificgravity, agronomic characteristics,quality traits, or disease ratings ineither of the two site-years.

Why were there no yield responses toB fertilization on low B soils in thisstudy? Are there other B sources toconsider? Let’s take a look at thepotential for irrigation water andsubsoil to supply B to crops.

Perhaps the irrigation water issupplying the necessary B to crops.A survey of 92 wells in northeasternColorado revealed an average of0.52 ppm B in the irrigation water,with a range from 0.03 to 2.30 ppmB. Based on 30 inches (2.5 ft) ofconsumptive water use by alfalfa, 0.3ppm B in irrigation water wouldprovide alfalfa’s required 2 lbs B/A

(2.5 acre-feet of water x 2.7 millionlbs water/acre-foot x 0.3 ppm B =2.0 lbs B/acre). Therefore, irrigationwater may be providing the necessaryB, thus preventing a response to Bfertilizer, even on soils testing low inavailable B.

However, the B level in the irrigationwater at both Yellow Jacket andCenter was only 0.02 ppm(equivalent to 0.1 lbs B/acre-foot ofwater), a level low enough to suspectthat a B fertilizer response couldoccur. Could subsoil B be supplyingthe B need for the crops grown inthese locations? This is a possibility inthe soil at Yellow Jacket; however, theshallow gravelly soils of the San LuisValley or the deep sands ofnortheastern Colorado don’t havemuch potential for subsoil storage ofB.

At this point, no confirmed Bdeficiencies have ever beendocumented in Colorado. Therefore,CSU does not recommend Bfertilization even on soils testing low inavailable B.

Jessica Davis, Susie Thompson, AbdelBerrada, Ron Meyer, and John Mortvedt

Extension Soil Specialist, Research Scientist,Extension Agronomist, and Faculty AffiliateColorado State University, San Luis Valley

Research Center, Golden Plains Area,Colorado State University

18 AGRONOMY NEWS

Sulfur Fertilization Of Dryland Winter Wheat

Sulfur increased yield when soil pH was high and OM was low.

In the 1980’s, CSU researchersHunter Follett and Dwayne Westfallstudied sulfur fertilization of winterwheat at 15 locations throughouteastern Colorado. Fertilizer treat-ments were injected about four inchesdeep at 12-inch spacings as liquidammonium thiosulfate about twoweeks before planting. The nitrogenand phosphorus applications wereuniform across the plots. Three of thefifteen locations had significant yieldresponses. However, the average soilsulfate levels in the responsive siteswas higher than the average level inthe non-responsive sites.

Many wheat farmers apply sulfur withtheir pre-plant nitrogen and phospho-

rus applications. Often the statedpurpose of the S is to reduce pH inthe fertilizer band (thus increasing theavailability of P, Zn, and Fe), notnecessarily to supply S as a nutrient.A closer look at the Follett andWestfall dataset reveals that the yieldresponse is related to the soil pH atthe 15 study sites. One of the re-sponsive sites had a low pH (6.6), butsulfur decreased yield significantly atthis site. The other two responsivesites had yield increases due to Sfertilization, and both had soil pHlevels of 7.5 or greater.However, there were two other siteswith pH of 7.5 or greater which didnot respond to S fertilization. Other

Soil pH Y ield R esponse De ta ils

< 7 .0 1/5 responsive sites T he responsive site had anegative y ield response.

7 .0 -7 .4 0/6 responsive sites --

> 7 .5 2/4 responsive sites T he responsive sites hadso il O M < 1 .5 % , and thenon-responsive sites hadso il O M = 2 .0 % .

research has shown that S fertilizerresponses are more likely to occur insoils with low organic matter contents.This principle holds true in this case aswell. The two sites with positive yieldresponse of 3-4 bu/acre both had soilpH levels > 7.5 and soil organicmatter levels < 1.5%. Therefore, Sfertilization has the best chance ofincreasing yield when soil pH > 7.5and soil OM < 1.5%. Be sure toconsider the cost of the additionalfertilizer when making your S fertiliza-tion decisions.

Jessica DavisExtension Soil Scientist

Colorado State University

Table 3. Wheat yield response to sulfur fertilization.

NOVEMBER-DECEMBER 2001 19

http://www.epa.gov/epaoswer/hazwaste/recycle/fertiliz/risk/EPA report on heavy metals in fertilizers.

http://animalscience-extension.tamu.edu/publications/13281133-ashoof.htmInformation on foot disorders in dairy cattle (Texas A&M University).

http://co.water.usgs.gov/trace/arsenic/USGS report and maps on arsenic in groundwater.

http://www.nrdc.org/water/drinking/qarsenic.aspFrequently asked questions (and answers) on arsenic in drinking water (Natural Resources Defense Council).

http://www.back-to-basics.net/Current soil fertility information from IMC and the Potash and Phosphate Institute.

http://www.ext.colostate.edu/pubs/crops/pubcrop.htmlColorado State University soil and fertilizer factsheet no. 0.545 Zinc and iron deficiencies.

web pages

20 AGRONOMY NEWS