Soil Health & Fertility

Healthy Soil Performs Five Vital Functions:• Regulates water - Soil helps control where rain, snowmelt, and irrigation

water goes. Water and dissolved solutes flow over the land or into and through the soil.

• Sustains plant and animal life - The diversity and productivity of living things depends on soil.

• Filters potential pollutants - The minerals and microbes in soil are responsible for filtering, buffering, degrading, immobilizing, and detoxifying organic and inorganic materials, including industrial and municipal by-products and atmospheric deposits.

• Cycles nutrients - Carbon, nitrogen, phosphorus, and many other nutrients are stored, transformed, and cycled in the soil.

• Supports structures - Buildings need stable soil for support, and archeological treasures associated with human habitation are protected in soils.

• To determine the level of nutrients found in a soil sample

• Accurate account of nutrient removal and replacement

• Crop production statistic• To manage fertilizer applications

Why We Need a Soil Analysis

A soil analysis is only as good as the soil sample submitted.

* Sample problem areas and good areas* Sample different soil types* Sample for different crops* Use appropriate sampling techniques- probe 6” to 7” for tilled soil- probe 4” for untilled soil- minimum of 1 sample per 20 ac.

• First Principle - Feed the soil and let the soil feed the plant.

• Second Principle – The fertility level we are working to achieve is the right amount of each nutrient. (Soil Balance)

• True soil balance means determining and adding the proper amount of each nutrient.

• Fertilizers must have a positive charge to be held to the soil colloid.

• Positive charged elements are called cations.• Colloids come from clay and organic matter

and carry a negative charge.• Negative sites on a clay particle will attract

and hold positives.

• Negatively charged elements such as nitrogen, phosphorus, and sulfur are called anions.

• Negative ions do not hold to the clay colloid and remain free to move in the soil solution or water.

• The first thing to do for your land is to correctly measure the amount of clay and humus the soil has in it.

• That measure is – cation exchange capacity, or CEC.

• CEC is a measure of the capacity of the soil to exchange nutrients or “holding power”.

• A CEC of 10 will hold twice as many pounds of nutrients as a CEC of 5.

First: You must know the total exchange capacity (capacity of soil to hold plant nutrients)

◦ < 15 Low CEC Sandy Soil ◦ 15 – 25 or Ideal CEC ◦ >25 High CEC Clay Soil

Soil Fertility

• What this means for us?– High levels of one nutrient can affect the uptake of

another nutrient– Example:

• Too much calcium in a soil can limit the uptake of potassium

• Too much potassium can limit the uptake of magnesium even if magnesium levels in the soil are high.

Cation Exchange Capacity

• Second: The base saturation percent (Specific % of nutrients needed for optimal plant growth)– What the soil is composed of in terms of cations

– calcium, magnesium, potassium, and sodium)– Also tells the availability of these nutrients to

plants• An excess of any one of these four makes it “the

weakest link in the chain”

Soil Fertility

Ideal for Ca & Mg is total 80%Clay soils need more Ca, sandy soils need

more MgCation Calcium should be 60% to 70%◦ 60% in sandy soils◦ 70% in clay soils

Cation Magnesium should be 10% to 20%◦ 20% in sandy soils◦ 10% in clay soils

Soil Fertility

• Yield and quality are determined by the percentages, not the pounds.

Calcium 60 – 70%Magnesium 10 – 20%Potassium 3 – 5%Hydrogen 10 – 15%Other Bases 2 – 4%

• Too much Calcium ties up all other nutrients (every other nutrient has to ride over the back of Ca to get to the plant).

• Too much Nitrogen ties up Calcium and other elements; even Zinc.

• Too much Phosphorus ties up Zinc and Copper.

• Too much Potassium ties up Boron.

Nutrient Imbalance

• pH refers to how acidic or alkaline the soil is.

• pH – potential Hydrogen• Range of 0 to 14 with 7 as neutral• A change of one unit in the pH scale

represents a 10-fold change in acidity or alkalinity

pH

• Affected by:– Fertilizers– Rain– Organic Matter– Soil microorganisms

pH

• Influenced by:– Calcium– Magnesium– Potassium– Sodium

pH

pH

Global variation in soil pH. Red = acidic soil. Yellow = neutral soil. Blue = alkaline soil. Black = no data.

• Limestone is the most effective and inexpensive aid to adjust soil pH.– Dolomitic limestone – magnesium and

calcium– Calcitic limestone – calcium

Lime

• Calcium influences pH, as does magnesium, potassium and sodium.

• Lime increases microbial activity, manages decomposition and overcomes the potential for Ca and Mg deficiencies.

Lime

• The pH will adjust to the proper level when all nutrients are corrected.

• Any nutrient required takes precedence over pH. When all nutrients are balanced, the pH will be right.

• As Ca concentration increases, it takes less nitrogen, phosphorus and potassium to do the same job.

• Every other nutrient has to ride over the back of calcium to get into the plant.

Organic Matter• Soil microorganisms decay organic matter and cycle nutrients

back into forms that plants can use.• The valuable link between soil carbon and your crop are soil

microorganisms.• OM effects nutrient cycles by chelating (chemically holding

on to) nutrients, and preventing them from becoming insoluble and therefore unavailable to plants

• Without microbes, vital soil nutrients like Phosphorus remain present but unavailable to your crop.

Enhanced development of soil aggregatesIncreased pore spaceIncreased infiltration and percolation ratesIncreased water holding capacity and…

Organic Matter

• Greater capacity to hold and release nutrients

• Nutrient storage• Improved cultivation ease (tilth)• Promotes further biological activity

Organic Matter

Five Ways Organic Matter Resists Soil Compaction

1. Surface residue resists compaction. It acts like a sponge to absorb weight and water.

2. Organic residues are less dense than soil particles.3. Roots create voids and spaces for air and water.4. Roots act like a biological valve to control oxygen in the soil.5. Roots supply exudates to glue soil particles together to form

macro-aggregates and supply food for microbes.

Organic Matter

HumusHumus refers to any organic matter that has reached a point of stability, where it will not break down any further.

Improves the structure of soil and contributes to moisture and nutrient retention.

Humus can hold the equivalent of 80-90% of its weight in water.

Allows soil organisms to feed and reproduce and is often described as the “life force” of the soil.

• Nitrogen– Part of every living cell; important

component of proteins, DNA, RNA– Directly involved in photosynthesis– Necessary component of vitamins– Aids in production and use of

carbohydrates

Nutrient Functions

Nitrogen

• Has a negative charge and attracts a positive charge.

• Excess N causes weakness in the plant.• Ties up copper and zinc.• Takes either sodium or calcium as a passenger.• For every % Ca taken out by N, Mg goes up 1%• Anhydrous Ammonia (free ammonia) is toxic

to living organisms and raises pH.

• Phosphorus– Energy exchange– Promotes early root formation and growth– Vital to seed formation– Increases water use and efficiency– Hastens maturity

Nutrient Functions

• Potassium– Essential for plant growth– Increases photosynthesis– Essential to protein synthesis– Improves quality of seed and fruits– Improves winter hardiness

Nutrient Functions

• Calcium– Continuous cell division and formation– Reduces plant respiration– Increases fruit set– Stimulates microbial activity

Nutrient Functions

• Magnesium– Key element in chlorophyll production– Improves utilization of Phosphorus– Activator and component of many plant enzymes

Nutrient Functions

Sulfur• 20 to 25 ppm minimum, 40 to 50 lb. of sulfur

per acre.• Adequate sulfur improves the palatability of

any crop.• Helps control excesses such as Mg and Na.• Sulfur must move with water to carry excesses

out.• Ca must be >60% for sulfur to work.

Sulfur Sources

• Elemental Sulfur• Ammonium Sulfate• Copper Sulfate

Sodium

• Anything above 3% is considered excess.• Proper Ca/Mg saturation can compensate for

higher saturations of sodium.

Zinc

• Probably the most universally helpful of all the micro-nutrients.

• Instrumental in moisture absorption.• 6 ppm minimum• Pecans and other nuts are Zinc sensitive.

Boron

• A minimum of 0.80 ppm is recommended.• Increases N availability to the plant.• Helps in nodulation of legumes.

• Soil Analysis reports are an important tool in managing nutrient removal and replacement.

• A Healthy Soil has a healthy biological system.• Organic Matter promotes further biological

activity.• Balancing soil nutrients is very important.• Calcium is important to microbial activity.

Summary