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Soil Fertility Management Credit to Fred Magdoff and Harold van Es
Building Soils for Better Crops
Characteristics of Healthy Soil Sufficient supply of nutrients to grow crop but not too
much. Good tilth: roots can fully develop & water may infiltrate
easily & be stored. Well drained: allow soil to be worked and oxygen to
reach root zone. Low populations of plant disease and parasitic organism Low weed pressure High populations of beneficial organism to promote
growth Free of chemicals that might harm plant such as soluble
aluminum Healthy soil should be resilient. What is the most important characteristic of a healthy
soil?
High % of Organic Matter
“Good soil organic matter management is the very foundation for a more sustainable and thriving agriculture”
Very Lifeblood of a healthy, productive soil
What is Soil?
Soil
Mineral Solids 48%
Water 30%
Air 20%
Organic Matter 1-6%
Mineral Solids
Sand Silt Clay They vary dramatically in size: Clay particle = head of pin Sand particle =BASKETBALL Clay many more surfaces more fertile many more pores between particles
Minerals
Silicon
Oxygen
Aluminum
Potassium
Calcium
Magnesium
Soil Water
Soil Solution contains dissolved nutrients made available to roots of the plant for growth
Main source of water for plants
Air
Allows plants to “breathe” that is provides the roots with oxygen.
Removes excess carbon dioxide from respiring root cells.
Organic Matter
Smallest constituent part of soil but the very foundation of its fertility and quality.
Key to sustaining soil productivity over time.
OM positive effect on soil’s Biological processes
Physical condition
Chemical condition
OM’s effect on Biological Processes
Provides CARBON
Carbon = food for microorganism
Releases nutrients in forms available to plants for growth
OM improves soils physical condition
Structure or tilth
Aeration
Drainage
Ability of roots to proliferate
Darker color warms up sooner
OM positive effect on soil’s chemical condition
Increase nutrient reserves
Retention of soluble nutrients
Buffer rapid change or toxic effects
Soil Organic Matter
The Living
The Dead
The Very Dead
The Living
15% of OM
microorganisms, earthworms & insects
Workers who do the breaking down of the dead OM helping release nutrients.
Sticky substances on earthworms and fungi help stabilize soil structure helping to bind particles together, stabilizing soil aggregates
The Dead
Fresh residues = recently deceased microorganisms,
insects,
earthworms,
old plant roots,
crop residues,
and manures
Their Decomposition = food for plants
The Very Dead
HUMUS = well decomposed OM.
No longer food for organisms
Reservoir for essential nutrients & their slow release to plants.
Large amounts of humus
Lessen drainage problems in clay soils
Improve water retention in sandy soils
Hydroponics vs. OM
Plant Nutrition
Nitrate Fertilizers Microorganisms
Carbon = once living animal/plant mater ORGANIC MATTER
Mineralization
Most nutrients in OM not available to plants as part of large organic molecules
Soil Organisms eat away (decompose) the large organic molecules releasing weak carbonic acids
nutrients are converted into simpler, inorganic, or mineral forms that plants can easily use.
For example: Proteins converted to ammonium NH4 & then to Nitrate NO3—soluble to plant roots.
Soil Fertility Management
Organic Matter Management
Assessing Nutrient Needs
Organic Matter Management Conserve it & Add Residues to Soil
Conservation of Soil OM
Avoid unnecessary tillage.
Rotavators make beautiful fluffy seedbed free of residue BUT harmful to soil structure. Cultivation & tillage promotes oxidation or “burning Up” of OM by microbes
Reduce soil erosion: by maintaining cover: cover
cropping, no-till cropping, or mulching.
Windbreaks: fences, trees, planting strips of cover crops.
Maintaining good soil OM
Addition of Organic Residues
We need to be constantly, annually adding OM.
Cover Crops
Manures
Composts
Crop residues
Contradiction
Need decomposition of OM Without it no nutrients made available to
plants.
No glue to bind particles is manufactured
No Humus is produced to hold onto to nutrients as water leaches through the soil.
Stop we don’t want too much OM to decompose least the soil become depleted.
Effects of Different Management Practices on Gains and Losses of OM
Management Practice Gains
Increases
Losses Decreases
Add material from off the field (manures, composts, other organic material
Yes No
Better utilize crop residue (burning crop residue)
Yes No
Include high residue producing crops in rotation (Sweet corn or Broccoli )
Yes No
Include sod crops (grass/legume forages) in rotation
Yes Yes
Grow cover crops Yes Yes
Reduce Tillage Intensity Yes/No Yes
Use Conservation Practice to reduce erosion
Yes/No Yes
What’s this all add up to? (Adding OM, reducing tillage)
Trying to overcome the inherently exploitive process of growing vegetables, of mining the soil.
Trying to keep fed those (microorganisms) that help to feed us.
If we break even on sandy soils, maybe increase a little doing well.
On clay soils may be able to increase but requires large inputs of OM.
Ultimate Goal: Use organic residues to meet the nutrient needs of crops supplementing with fertilizers only when necessary.
AMBITIOUS!!! For example . . . .
But what if the soil is cold?
No Microbial Activity
No Mineralization
No plant growth
Early Spring crops planted on cool, wet soils need soluble forms of nutrients—fertilizers.
Nutrients from Crop Residues not Sufficient to meet Crop needs
1. Soils have inherently low levels of a Crops are grown on compacted soils or otherwise physically sub par.
2. Nutrients such as P or K reserves need to be built up.
3. Quantity of residue applied not sufficient.
4. Nutrient availability from residue & timing of crop uptake do not coincide.
Assessing Nutrient Needs
“Assessing nutrient needs for optimal crop production is essential to the appropriate use of fertilizers.” Vern
Soil Tests and Tissue Tests are the tools.
Soil Tests monitor soil characteristics: Organic Matter level
Soluble salt content
Nutrient ratios
Tissue Tests:
How to Sample?
Performed every 3 years
In each field treated as a unit
Collect sample by = 12” soil probe
randomly collecting small samples,
across the area of concern,
To a depth of the “bulk” of the plant’s roots.
Put in plastic bucket and mix
Measure out one cup taking 10-15 spoonfuls and put in a plastic zip-lock bag.
The Lab
The test is performed in a laboratory
Treat the soil with weak acid solution to extract & then analyze the nutrients.
Stick with one lab b/c different labs use different extraction procedures.
The results can not be safely compared
Results are only an index of nutrient availability and not exact quantities.
Soil pH—6.0
Due to climate and rock-types in which the soils of New England have formed, soils here tend to be naturally very acidic (4.5-5.5). Not naturally conducive to growing vegetables.
What is pH?
A measure of soil acidity is a primary factor in plant growth.
The pH scale expresses the amount of free Hydrogen (H+) in the soil water.
The lower the pH the more acidic the soil.
A pH of 7.0 = neutral
The scale is logarithmic: a pH of 6.0 is ten times more acid than 7.0
Why is the proper pH important?
Why is the proper pH ! Low pH below 6.0 or acidic soil causes:
Availability of plant nutrients is reduced N, P, K are less available or lost through leaching Indication that Ca & Mg are low May be toxic levels of I, Al, & manganese Bacterial activity decreases
Soil pH is naturally lowered over time by a variety of chemical reactions that result from microbial activity which include: Process of Mineralization:
Transformation of ammonium to nitrate Sulfur to sulfate Formation of carbonic acid from carbon dioxide and water Production of organic acids.
The soil needs pH of 6.5-6.8/slightlly acidic for optimum utilization of nutrients.
How do we adjust the pH?
We apply limestone = Calcium Carbonate CaCO3
Liming materials vary in their ability to raise soil pH depending on their Ca & Mg content
The fineness of the grind
The proportion of Ca & Mg content that is in the form of oxides or carbonates.
Limestone with high Mg content is called dolomitic lime
Apply no more than 4 tons per acre at once or “shock” the soil and tie up trace elements like B
Soils high in OM or clay are more buffered against chemical changes and require more lime to change pH.
If soil is alkaline – above 7.0, then use Sulfur to low it.
What Happens when we lime?
The lime neutralizes H and Al with Ca and Mg. As H+ on humus is neutralized by liming, the
site on the soil particle (colloid) where it was attached now has a negative charge and can hold Ca++. Mg++, K+ and minor nutrients.
The lime-calcium carbonate chemically reacts
with H & Al and “kicks it off” the microscopic soil particles making the site available to the other nutrients.
Cation Exchange Capacity (CEC)?
Describes the ability of a soil to hold on to positively charged ions (cations) such as Ca++, Mg++, K+, NH4+
CEC measure the soil’s ability to retain and to supply nutrients.
The bulk of this capacity resides in finely divided soil OM. A smaller amount from the soil’s clay particles; hence clay soils
naturally more fertile.
CEC is ! b/c the primary reservoir of readily available K, Ca, Mg and several micronutrients.
“Effective CEC” is based on the soil test quantities of Ca,
Mg, & K. It relflects the ability of the soil to “hold” these cations. A normal range is from below 5 in sandy soils low in OM to over
20 in clayey soils or those high in OM
Base Saturation Ratio Ca:Mg:K ratio
Describes the relative proportion of Ca, Mg, & K cations that are held by soil particles.
A wide range is acceptable, but an ideal ratio is 20:4:1 in soils above pH 6.0
Mine is 13: 1.7 : 1. or 58.4% Ca, 8.2% Mg & 4.8% K. What’s ! Don’t try to achieve ideal numbers—too
expensive. BUT pay attention to the balance of nutrients esp. Mg & K Avoid Excess of one nutrient that may suppress the uptake of
another.
Use the Info to help select fertilizer materials to adjust the ratio in the desirable direction.
Aluminum indicator of both lime and phosphorus needs
Major and Minor Nutrients or what plants need to eat to stay healthy
• Primary Nutrients • Nitrogen • Phosphorus • Potassium
• Secondary Nutrients • Magnesium • Manganese • Copper
• Minor or Micronutrients • Zinc • Iron • Sulfur • Calcium • Molybdenum • Boron
Nitrogen (N)
Gives dark green color to plant. Increases growth of leaf and stem. Influences crispness and quality of leaf crops. Stimulates rapid early growth.
Deficiency Symptom: Light green to yellow leaves. Stunted Growth
Excess Symptom: Dark Green, excessive growth. Retarded maturity—maintains vegetative growth. Loss of buds or fruit.
Phosphorous (P)
Stimulates early formation and growth of roots. Gives plants a rapid and vigorous start. Is important in formation of seed. Gives hardiness to fall-seeded grasses and grains.
Deficiency Symptoms: Red or purple leaves (often a result of cold soil temperatures). Cell division retardation.
Excess Symptoms: possible tie up of other essential elements. Don’t worry.
P cont.
Naturally low in many soils; soils with a history of agricultural use often have P reserves.
Due to cold soil temps, plants not efficient at taking up P when soils cold. Aids in early season growth to band or fertigate small amount of P. near the
roots Use Super Phosphate which has been chemically treated with acid Super-
phosphate makes it soluble and available to plants.
Organic farms low in P have costly problem. Rock Phosphate may contain up to 30% phosphate, but very slowly available –only about 2% P2O5. Need large quantities. Colloidal or Soft = 3%. Bone meal contains more but more expensive. Manure & composts contains only small amounts but regular use will build
reserves up.
Potassium (K)
Increases vigor of plants and resistance to disease. Stimulates production of strong, stiff stalks. Promotes production of sugar, starches, oils. Increases plumpness of grains and seed. Improves quality of crop yield.
Deficiency Symptoms: Reduced vigor, susceptibility to diseases. Thin skin and small fruit.
Excess Symptoms: Coarse, poor colored fruit. Reduced absorption of Mg and Ca.
K cont.
Heavier Soils with more clay = large K reserves. Sandy Soils = little reserves. K prone to leaching esp. with low CEC. Potassium chloride (muriate of potash) 0-0-60, a natural salt = common K
source. Being a salt and soluble can dehydrate or burn roots.
Sul-po-mag (potash of sulfate magnesia)0-0-22-11 Mg is excellent source for soils low in Mg.
Manure and compost are important sources of K. Use over time will boost soil reserves.
Wood ashes must be used with caution. They are alkaline raise pH rapidly and are high in soluble salts & may burn roots.
Naturally occurring Chilean nitrate (nitrate of soda-potash) 16-0-14 may be used on organic farms as long as only 20% of a crops total N.
Magnesium (Mg)
Aids photosynthesis. Key element in chlorophyll. Deficiency Symptoms: Loss of yield. Chlorosis of old
leaves. Excess Symptoms: Reduced absorption of Ca & K. Most economical source is dolomite or high-mag lime.
Use if liming required. Liming not required but K is, use Sul-po-mag 0-0-22-
11Mg. Epsom salts 0-0-0-10 Mg may be used in K not required Emergency foliar sprays of Epsom salts are used to
alleviate deficiencies in tomatoes, spinach, or celery.
Calcium
Essential in the proper functioning of plant cell walls and membranes. Sufficient Ca must also be present in actively growing plant parts, especially storage organs such as fruits and roots.
Part of enzymes (proteins that act as catalyst for chemical reactions).
Deficiency Symptoms: stops growing point of plants. Excess Symptoms: Reduces the intake of K and Mg. Usually sufficient amounts supplied by liming in order to
maintain proper pH. Use calcium nitrate (CaNO3) 15-0-0 to maintain good
supply of available Ca to “soft-fruited” crops like tomatoes, peppers, melons and berries.
Trace or “Minor” Elements
Boron (B) = Affects absorption of other elements
Copper (Cu) = enzyme activator
Iron (Fe) = a catalyst in the enzyme system
Manganese (Mn) = in enzyme system.
Sodium (Na) = present not sure of its function
Sulfur (S) = helps build proteins
Zinc (Zn) = aids in cell division
Trace elements cont.
Needed in very small quantities
Deficiencies are not common
Supplied in sufficient quantities by organic residues such as manure, compost, & cover crops.
Soil test = Alert if potential problem
Except for Boron, I don’t worry Boron important in Cole crops such broccoli.
% Organic Matter excellent for sandy loam
Nitrogen Management
Soils tests not reliable indicators of N Available N fluctuates during growing season
depending upon: Environmental conditions
Microbial activity
Like trying to measure temp of soil for entire growing season from single measurement.
Pre-sidedress N test for corn is a useful predictor of N fertilizer needs b/c single measurements have been correlated with subsequent N availability. Single snapshot for the moment of what is there
Pre-Sideress N test for Corn
is a useful predictor of N fertilizer needs b/c single measurements have been correlated with subsequent N availability. Single snapshot for the moment of what there is
and what will be needed over short period of time.
Explicit protocol: Corn 6-12 inches
Soil sample to depth of 12 inches
Dried promptly to stop microbial activity
Rapid delivery to lab.
Nitrogen Budget
Vegetable crops require 50-200 lbs. of N per acre in the Northeast.
Recommendations for specific crops are
in New England Vegetable Management Guide.
in soil test recommendations.
Nitrogen Budget cont.
Start with the total N. needed for the Crop: Subtract release of N from soil organic matter Subtract manure and compost applications Subtract legume plow downs
The Difference is the amount of N. which needs to be applied in fertilizer. Too little N. = reduce crop yield andquality Too much N. or applying at the wrong time =
Threatens water quality by leaching Wastes $$$$$ Reduce the yield & quality of certain vegetables usually fruiting ones by
promoting excessive foliage growth (too vegetative) or suppressing fruit development
When to Apply N.
N requirements for most crops are greatest when the growth rate is greatest.
General rule the growth rate is greatest +/- one month after seed emergence or transplanting.
Side-dressing soluble N. is most efficient at this time: 30-40 lbs per acre of N.
Calculating the amount of a Material to Apply at Side-dressing
Application rate = 30 lbs of N. per acre
Urea = 46-0-0 per 100 lb bag.
How lbs of urea do we need to apply?
46/100 = 30/x
46x = 3000
X = 3000/46
X = 65 lbs.
Animal Manure as N. source
Not all of the N. in animal manure is available the first year it is applied b/c OM breaking down, slower release, carbon/n.
About half of it or around 5-6 lbs of N per ton from cow manure are available
N contribution highly variable Manure’s composition--bedding, urine, feces. Handling--age and amount of exposure to air and rain Moisture content—put on more or less depending upon weight.
20 tons of Cow manure per acre may meet or exceed N requirements for many crops
Release on N from manure continues for many years although it declines each year.
Can have the manure tested for nutrient content
Green Manure as N source
Cover crops—strong stands of legumes, clovers, alfalfa, or hairy vetch plowed under release up to 100 lbs per acre of N.
Remember legumes fix N from the atmosphere through bacteria in their root nodules
Compost as N source
“The release of N from compost is a less clear matter”. Vern
Very mature compost the release may be only slightly greater than from soil OM which each year is only a few % of the total N it contains.
The less mature compost = b/w OM and manure
Compost analysis should be done to get good estimate of N availabilty.
N release from Soil Organic Matter
For each 1% of OM = 10 lbs. of N per acre will be available to vegetable crop.
Applying Fertilizer
Nutrient needs for an Acre of Cabbage
Spring planting
Summer planting
Plow down Hairy Fescue
Apply 20 tons Cow Manure
Apply Nothing as far as OM
Chemical Fertilizersl;
Organic Soil Amendments