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 1 unit of Nitrogen Paper 170:1 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