Building Soil Health: Key to Organic Soil Fertility Management

John Idowu Extension Plant Sciences

NMSU, Las Cruces Email: jidowu@nmsu.edu

Phone: 575-646-2571

Difference between Conventional and Organic Soil Fertility Management

• Conventional Systems:

– The plant/crop is the direct target

– Immediate short-term productivity

– Environmental conservation in some cases is of secondary concern

– Quick fixes for immediate maximum productivity

– Same system is repeated yearly to maintain productivity

– Not much interest in diversity

Difference between Conventional and Organic Soil Fertility Management

Organic Systems:

• Feed the Soil to Feed the plant – Adding organic materials such as cover crops, crop

residues, and composts to cultivated soils over time

– This will build soil organic matter and improves the ability of the soil to supply nutrients

• Organic soil fertility is highly dependent on Soil Health

Organic Soil Management Strategy

• The ultimate goal is a healthy, fertile, biologically active soil

with improved structure and enhanced nutrient availability.

• As soil organic matter increases, nutrients are incorporated

into the soil, allowing the soil to act as a reservoir of these

and other nutrients.

• The decomposition of soil organic matter releases nutrients,

at which point they become available for plant uptake.

What is Soil Health?

• Ability of the soil to support crop growth … (Power &

Myers, 1989)

• Capacity of the soil to function in a productive and

sustained manner … (NCR-59 Madison WI, 1991)

• The capability of the soil to produce safe and

nutritious crop …. (Parr et al., 1992)

• Fitness for use (Pierce & Larson 1993)

Chemical

Physical Biological

Soil Health

Approach to Soil Health

Components of Soil Health

Physical Fertility

Biological Fertility

Chemical Fertility

Soil Health Indicators

Physical Chemical

Biological

• Cation exchange

capacity

• N, P, K

• Salinity

• Micronutrients

• [Toxins, pollutants]

•Bulk density

•Penetration

resistance

•Aggregate

stability

•Water infiltration

rate

•Water holding

capacity

•Pore size

distribution

• Soil disease suppressive

capacity

• Beneficial and pathogenic

nematodes, [other pathogens]

• N mineralization rate (PMN)

•Decomposition rate

•Respiration rate

•Earthworm counts

•% OM

• “Active” C, N in OM

Physical Issues

• Soil Texture – Relative distribution of

Sand, Silt and Clay

• Soil Structure/Agregation – how well

the soil binds together

• Soil Density – how tightly the soil is

packed together

Soil Texture = %Sand, Silt & Clay in a soil

• Soil texture is the single most important physical property

of the soil. Knowing the soil texture alone will provide

information about:

1) Water flow

2) Water holding capacity

3) Fertility potential

4) Suitability for different crops

• The arrangement of soil particles into

aggregates of different shapes and size

– How is the distribution of aggregates?

– How stable are the aggregates?

– How is the configuration of the pores?

Soil Structure

Aggregation

Affects Soil erosion by water and wind

Pore size distribution (water movement/retention)

Drought tolerance of soils

Root growth and proliferation

Soil aeration

• Clay content

• Chemical elements associated with the clay

• Products of decomposition or organic matter

• Microbial population

Factors Affecting Aggregate Stability

Aggregation as a function of soil management

Soil Density

Affects

Water movement

Water holding capacity

Root growth and proliferation

Soil aeration

Root Growth and Compaction

Definition: The resistance of a soil to root growth

Affected by Density of

Soil:

Low Bulk Density and high

porosity make soil easy to

penetrate

Deep Loose Soil

Compacted Soil

Roots in loose or compacted soil

Compaction Assessment

PENETROMETER can be used to identify compaction layer in the soil

- Take measurements when the soil is at field capacity

Quick and Cheap Assessment

DIG with a shovel

Solving Compaction Problem?

Very difficult task

Method 1

Soil loosening with tillage equipment OR Manual digging

in a small garden

• Require a lot of energy to achieve

• Does not bring the soil totally to pre-compacted

state

Method 2

• Use deep rooted crops to loosen the compact

layer, examples: alfalfa, forage radish,

• Takes more time to become effective

Best is to combine both methods

Tillage Radish – Biodrilling

Biological aspects of soil health

–Diversity of Flora and Fauna

–Soil Microbial Activity

–Organic Matter Decomposition

–Amount Soil Organic Matter

–Soil Borne Pathogens

Soil Organisms

• Those we can see with our eyes • Earthworms

• Insects

• Burrowing animals

• Those we cannot see with our eyes • Bacteria

• Fungi

• Actinomycetes

• Nematodes

• Protozoa

Location of microbes in Soil

• Mostly in top inch

• Almost all in top 6 inches

• Rhizosphere

– Zones close to the roots

– Region of intense activity

– Stimulus: Secretions from roots

Root exudates (including other losses) can account for 10 to 33% of the net plant photosynthetic product.

Soil Microorganisms

Organisms that we cannot see with our eyes

(Micro means “very small”)

• Bacteria (Often Single Cell)

• Fungi (Often Long Filaments or Hyphae)

• Actinomycetes (Properties of Both)

Bacteria

• Bacteria are very tiny, one-celled organisms that aren't plants or animals.

• They are much simpler than plants and animals.

• They can be shaped like a grain of rice or have other shapes.

Examples of legumes are alfalfa, clovers, beans

Bacteria that make nitrate in plant roots with plants are called Rhizobium

Nitrogen come from the soil air (79% N2 in soil)

It is a relationship of give and take (Symbiosis)

Plants supply bacteria with food and bacteria gives back nitrate to plants

Can fix up to 300 kg/ha N (270Ibs/ac N) in a year

Nitrogen Fixation in Legumes (making nitrogen available to crops)

Nodules Root

Sesbania Nodules (Grown as summer green manure in Las Cruces)

Mineralization: Breakdown of Organic Matter

• Organic materials are full of nutrients that can help crops

grow in the field. Example of such nutrients include:

– Nitrogen, phosphorus, sulfur

• Example of organic materials are:

– Cow manure, dead leaves and plant residue, compost, chicken

manure, etc.

• Mineralization is the release of these nutrients in forms

that growing crops can use

How does soil mineralization happen?

As the microbes feed on soil organic matter, nutrients are released

Microorganisms

(bacteria, fungi and others)

Small and large animals

(earthworms, bugs, nematodes) Fertile soil with

nutrients will

produce good crops

NO3

P S

Mg K

Ca

Decomposition of OM dependent on

Temperature (Low in winter high in summer)

Moisture (problems – too dry or too wet)

Food Supply (Amount of Organic Matter)

Oxygen (problem – low O2)

C:N Ratio (next slide)

Material C:N Ratio

Wood chips 700:1

Sawdust or pellets 500:1

Paper 170:1

Straw, wheat 130:1

Bark 100:1

Straw, oat 80:1

Leaves 60:1

Cornstalks 60:1

Peanut hulls 50:1

IDEAL RATIO 30:1

Fruit waste 35:1

Legume grass hay 25:1

Grass clippings 19:

Poultry house litter, stockpiled 15:1

Yard waste 14:1

Fresh manure, cattle 8:1

Fresh manure, swine 6:1

Fresh manure, poultry 6:1

700 units of Carbon to 1 unit of Nitrogen

30 units of Carbon to 1 unit of Nitrogen

More N available

Less N available

Carbon to Nitrogen Ratio

Fungi

• Fungi are primitive plants that don't have chlorophyll (they can’t make their food from the sun)

• The multiply with thread-like structures called Hypha

• They are mostly saprophytes – secrete enzymes for digestion before uptake

• Tolerant of acidity

• Important decomposer of lignin (hard to decompose part of plants)

Fungal Association

• Some types of beneficial fungi that can grow

on plant roots are called Mycorrhizae

• Mycorrhizae fungi have many filaments that are like thin hairs around the roots

Benefits of Mycorrhizae

• Mycorrhizae fungi helps the plant get food (nutrients) and water from the soil

• The plant makes carbohydrates and gives some to the mycorrhizae fungi for energy.

• The fungi help the plant and the plant helps the fungi

Positive Roles of Microbes

• Mineralization (making nutrient available from organic matter)

• Nitrogen fixation (making nitrates available from Nitrogen in soil)

• Aggregate stabilization (making soil structure better)

• Predation on pests and pathogens (making soil able to resist diseases)

× Immobilization: (making nutrients unavailable to crops)

× Denitrification: (removing nitrates from the soil and converting it back to nitrogen air)

× Pathogens: (microorganisms can attack plants making them less productive)

Negative Roles of Microbes

Other important soil organisms

Nematodes: Not all of them are bad!

• Worms that are microscopic in size

• Most abundant soil animal

• Involved with nutrient cycling (Beneficials) • Live in water films surrounding soil particles or in

plant roots

• Encyst in dry soil and repopulate when conditions are favorable

• Parasitic nematodes have stylet and are more mobile than beneficials

• Upon infection of host plants the react by forming galls, knots or deformed roots.

Other Soil Animals

• Nematodes

• Springtails

• Mites

• Insects

• Earthworms

Earthworms

• They eat dead plants and break them down for microbes

• They mix the soil by moving materials form the surface down into the soil and this helps nutrient distribution

• They help water to flow through the soil

• They help soil to form better structure

• Their channels allow roots to grow well into the soil

• Percentage small (often <5%) but has very great effect on soil productivity

– Food for soil organisms

– Influence physical, chemical and biological properties

– Enhance soil fertility (make soil more fertile)

– Helps soil hold more water

– Make soil more stable against erosion

Soil Organic Matter – Driver of Soil Health

Other benefits of organic matter

• Impart favorable chemical and physical attributes

– Increases cation exchange capacity [CEC] (K+; NH4

+; Mg++ and Ca++)

– Organic matter can increase CEC by 20 -70% of the total CEC

– SOM enhances nutrient cycling by providing habitat for diverse soil organisms

Other nutrients supplied by organic matter

• Organic matter is a good source of nitrogen phosphorus and sulfur

• Organic matter is also a significant source of micronutrients such as iron (Fe), copper (Cu) and zinc (Zn).

Estimating the amount of N available from the soil organic matter

• Total N is about 7% of the soil organic matter

• 2% of the total nitrogen is mineralized per year

• 6 inches of soil weighs 2,000,000 pounds

How much N from organic matter

> If we have 1% soil organic matter (SOM)

> For estimating N, we use 12 inches of soil

> 12 inches = 4,000,000 lb. of soil

> SOM in 12 inches = 0.01 x 4m = 40,000 lb.

> Total N = 40,000 x 0.07 = 2,800 lb.

> With 2% mineralization rate per year:

> 2,800 x 0.02 = 56 lb. nitrogen per year

Active Fraction

• 10 to 30% of the soil

organic matter (active

fraction) is responsible

for maintaining soil

microorganisms.

• The active fraction of

organic matter is most

susceptible to soil

management practices.

ACTIVE

Humus Facts

• Humus is the most resistant and mature fraction of soil organic matter.

• It is very slow to decompose and may last for hundreds of years.

• Plant residues that are high in carbon (C) and low in nitrogen, such as straw or cornstalks, decompose slowly but are efficient producers of humus.

• Residues that contain high levels of nitrogen, such as young cereals and legumes, decompose quickly, producing less humus.

Chemical aspects of soil health

–Nutrient sufficiency

–Soil salinity levels/Sodium issues

–Water salinity levels

Nutrient Sufficiency

Very basic and important for crop growth

Requirement is species dependent

Knowing the nutrient status of the soil before cropping

will help in calculating how much to add

Soil testing will help determine how much to add

Nutrient deficiency can occur at any stage

Essential Elements for Growth

A Total of 16 Elements

Resolving Chemical Issues

Soil Testing is Important !!!

– Helps to know what is in your soil

– Helps to plan how much of nutrients to apply

– Nutrient needs vary with soil and crop

– Helps to know if your soil is building up salts

– Will let you know if your management is improving,

degrading or maintaining your soil

Which Lab Do I Choose?

• Go to NMSU site (www.nmsu.edu)

• Type “Labs for New Mexico Soils” in the search

• Click on the link “Labs for New Mexico Soils”

• Go to the website of the lab you have chose

• Make sure you check their sampling protocol and costs

• Stick with the same lab to be able to compare results

Challenge of Organic Soil Fertility Management

• Timing and amount of mineralization often do not coincide with crop need

• This lack of synchrony between nitrogen mineralized from organic matter and crop nitrogen uptake is a major challenge for fertility management in organic systems

Timing of nitrogen (N) mineralization from soil organic matter, cover crop residue, and organic fertilizer in relation to crop N uptake (from Gaskell et al., 2006).

Determining nutrient needs

• Two key elements are necessary

– Crop Nutrient requirement

– Soil nutrient levels

• Application in excess of what the crop may need may lead to losses

• Nutrient availability in soils can vary radically with soil types

Crop nutrient requirements

Low total N content Medium total N content High total N content < 120 lb/acre 120–200 lb/acre > 200 lb/acre

baby greens carrot broccoli

beans corn, sweet cabbage

cucumbers garlic cauliflower

radish lettuce celery

spinach melons potato

squashes onion

peppers

tomatoes

Vegetable Crops and Maturity

Crop Time to Maturity

Radishes 1 - 2.5 months

Okra 1.5 - 2.5 months

Turnips 1.5 - 2.5 months

Squash 1.5 - 3 months

Peas 2 months

Potatoes 3 - 5 months

Spinach 3 months

Carrots 3 months

Peppers 4 - 5 months

Tomatoes 4 - 5 months

Watermelons 4 - 5 months

Cabbage 4 - 5 months

How Much is my Green Manure Contributing?

• From research done in CA, green manure growing for 4 to 6 months will add between 100 – 200 lb. /ac nitrogen

– Rapid N-release occurs 3 – 6 weeks after incorporation for materials with low C:N ratio

– Short season vegetables will benefit from green manure

– For longer season crops, more N will be needed later in the season

Planting should be done soon after green manure termination

• Significant amount of N can be lost if planting is delayed after green manure incorporation

• Recent study showed leaching losses of up to 50 lb N/ac following green manure incorporation after 11 inches of rain.

Photo from Cornell Waste Management Institute

What is composting?

Using the natural process of decay to change organic wastes into a valuable soil amendment

Benefits Contains slow release nutrients

for crop growth Help soils to hold more water Stabilizes soil structure Loosen tight clay soils for soil

quality improvement Improves sandy soils by

enhancing nutrient and water holding capacity

Compost

Turning Trash to Treasure

Compost

• Compost can be an effective source of nutrients (macro- and micro nutrients)

• More effective if they contain animal manure

• To get the best from compost you need to – Know the composting process (poor composting

delivers poor compost)

– Raw materials used (compost is as good as the material used)

• Compost with C:N < 20 will deliver nitrogen to the soil.

Important compost characteristics

• Age

• pH

• Salt concentration

• Purity

• Weed seeds?

Aged Manure

• Leaving manure in a pile for at least one year

• Provides valuable nutrients for crops

• Wait at least 120 days after applying raw or aged manure to harvest crops that grow in or near the soil (root crops, leafy greens, strawberries)

• Wait at least 90 days for other crops

• Safer to use composted manure

Peat Moss

• Improves soil moisture retention

• Minor improvement to nutrient holding capacity

• Provides negligible nutrient benefit

• High proportions may make soil hydrophobic

Materials to Avoid

Sawdust, wood shavings, wood chips

very high carbon/nitrogen ratio

will tie up all available N during breakdown (immobilization)

Worst when tilled in

minor detrimental effect if used as mulch

Commercial Organic Fertilizers

• Organic fertilizers are important for supplementing N mineralized from SOM, GM, and compost. They are particularly important in supplying late-season N to optimize crop yield and quality.

• Before using any unfamiliar product, please check with you certifying agency.

Commercial organic fertilizer

• Mostly by-products of fish, livestock and food processing industries

• Commercial formulation and nutrient analyses vary considerably

• Can be expensive

• Useful in situations where application of cover crops, compost cannot meet the crop requirements

• Relative rapid availability of nutrients

Commercial Organic Fertilizers

Materials Nitrogen

(%) Phosphorus

(% P2O5) Potassium

(% K2O)

Chilean nitrate ? (≤ 20% of N) 16 0 0

Blood meal 12 0 0

Feather meal 12 0 0

Fish meal or powder 10–11 6 2

Seabird and bat guano 9–12 3–8 1–2

Meat and bone meal 8 5 1

Soybean meal 7 2 1

Processed liquid fish residues 4 2 2

Alfalfa meal 4 1 1

Pelleted chicken 2–4 1.5 1.5

Bone meal 2 15 0

Kelp <1 0 4 Soft rock phosphate (not effective for high pH soils) 0 15–30 0 Potassium-magnesium sulfate (mined source & untreated) 0 0 22

77oF 59oF

Nutrient content of organic materials

To apply organic fertilizer correctly

• You need to test the soil

• You need to know how much your crop needs

• You need to test the organic material or know the composition of the organic material

• You need to know the critical period when crop nutrient demand is highest

Compost Analysis Report

Cover Crops – N supply capacity

• Depends on specie of cover crop (Grasses vs legumes)

• Depends on maturity at termination

• Depends on weather it is tilled into the soil or left on surface

• Depends on C:N ratio of cover crop

• Depends on the crop planted after cover crop (short season vs. long season)

Sesbania (Sesbania exaltata)

March-July

40-50 lbs/acre

- Very High Biomass 12.7 t/ac

- Good nitrogen fixation

- Excellent Weed Suppression

- Easy to Manage

- Sandy & Clay Soils

Las Cruces Cover Crop Trial

LABLAB COWPEA

Las Cruces Cover Crop Trial

Barley after sesbania summer legume

Oats after sesbania summer legume

Wheat after sesbania summer legume

Rye after sesbania summer legume

Soil Salinity Levels

Soil salinity can affect the growth and development

of trees

High salinity can lead to productivity decline and

eventual death of trees

To assess salinity, you need to do soil testing

Salinity Measurement

Salinity Class Non-saline Low Moderate High Severe salinity

Approx. soil salinity, ECe (dS/m)

0-2 2-4 4-8 8-16 >16

•Soil test result will report the Electrical Conductivity of the soil

Possible Solutions

Leaching of salts with extra water may be needed to correct salt problems

Some soil testing laboratory will give you the leaching requirement (amount of extra water needed to leach out the salts)

Planting salt tolerant species is another option to overcome salinity

Soil Salinity

Soil salinity: Crop and Soil Effects

Increase the osmotic potential of the soil

Toxic effects on the plant by affecting the opening of

stomata

Crop Tolerance to Salinity

Sodium Problem

• Laboratory measurements will clarify if you have sodium problem

• For sodium problem to be present, the Sodium adsorption ratio (SAR) must be greater than 13

Effect of Sodicity on Soil

• Sodium problem leads to dispersion of soil resulting in loss of structure

• Water will not be able to enter or move through the soil adequately

Correcting Sodium Problem

• Addition of ions to displace Na from clays

• Ca is the usual ion used to displace Na

– Gypsum (CaSO4) [Na2CO3 + CaSO4 = CaSO3 + Na2SO4]

– Calcium chloride (CaCl2) [Na2CO3 + CaCl2 = CaCO3 + 2 NaCl]

– Sulfur (if sufficient lime is in the soil)

S SO3 H2SO4 + CaCO3 = CaSO4 + H2O

• Leach out the sodium salts

• Adequate drainage is required

Leachable

Thanks!