Building Soil Health: Key to Organic Soil Fertility Management

John Idowu Extension Plant Sciences NMSU, Las Cruces Email: [email protected] 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) Approach to Soil Health

Soil Health Chemical

Biological Physical Components of Soil Health

Chemical Fertility Physical Fertility

Biological Fertility Soil Health Indicators

• Bulk density • Cation exchange • Penetration capacity resistance • N, P, K • Aggregate stability Physical Chemical • Salinity • Water infiltration • Micronutrients rate • [Toxins, pollutants] • Water holding

capacity • Pore size distribution Biological

• Soil disease suppressive • Decomposition rate capacity • Respiration rate • Beneficial and pathogenic • Earthworm counts nematodes, [other pathogens] • % OM • “Active” C, N in OM • N mineralization rate (PMN) 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 Soil Structure

• 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? Aggregation Affects .Soil erosion by water and wind .Pore size distribution (water movement/retention) .Drought tolerance of soils .Root growth and proliferation .Soil aeration Factors Affecting Aggregate Stability

• Clay content

• Chemical elements associated with the clay

• Products of decomposition or organic matter

• Microbial population 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

Compacted Soil

Deep Loose 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. Nitrogen Fixation in Legumes (making nitrogen available to crops)  Examples of legumes are alfalfa, clovers, beans  Bacteria that make nitrate in plant roots with plants are called Rhizobium Nodules

 Nitrogen come from the soil air

(79% N2 in soil)

 It is a relationship of give and take

(Symbiosis)

Root  Plants supply bacteria with food and bacteria gives back nitrate to plants  Can fix up to 300 kg/ha N Sesbania Nodules (Grown as (270Ibs/ac N) in a year 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)

NO3 K Mg

Ca S P

Small and large animals (earthworms, bugs, nematodes) Fertile soil with nutrients will produce good crops 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) Carbon to Nitrogen Ratio Material C:N Ratio

Wood chips 700:1 Less N available Sawdust or pellets 500:1 700 units of Carbon to Paper 170:1 1 unit of Nitrogen Straw, wheat 130:1 Bark 100:1 Straw, oat 80:1 Leaves 60:1 Cornstalks 60:1 Peanut hulls 50:1 30 units of Carbon to 1 unit of Nitrogen IDEAL RATIO 30:1 More N available 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 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) Negative Roles of Microbes ×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) 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 Soil Organic Matter – Driver of Soil Health • 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 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. ACTIVE • The active fraction of organic matter is most susceptible to soil management practices. 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. Compost

What is composting?

Using the natural process of decay to change organic wastes into a valuable soil amendment Turning Trash to Treasure 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 Photo from Cornell Waste Management Institute 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

Nitrogen Phosphorus Potassium

Materials (%) (% P2O5) (% 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) Las Cruces Cover Crop Trial 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 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

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

Salinity Class Non-saline Low Moderate High Severe salinity Approx. soil salinity, ECe 0-2 2-4 4-8 8-16 >16 (dS/m)

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

Leachable – 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

Thanks!