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