organic fertility management organic fertility management is much more than adding nutrients into...

Download Organic fertility management Organic fertility management is much more than adding nutrients into the soil. Overall goal is to balance nutrient inputs

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  • Slide 1
  • Organic fertility management Organic fertility management is much more than adding nutrients into the soil. Overall goal is to balance nutrient inputs and outputs and ensure a good balance of nutrients for the crop to achieve this requires a complex mix of soil management activities including tillage, irrigation, residue management, weed management and crop rotation planning Neglecting any of these components can compromise crop performance.
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  • What is meant by soil fertility and soil quality? Soil fertility is the capacity of a soil to provide nutrients required by plants for growth, and is one component of soil quality. Soil quality is a broader concept that can be defined as the capacity of the soil to: Accept, hold, release and mineralize nutrients and other chemical constituents Accept, hold and release water to plants, streams, and groundwater Promote good root growth and maintain good biotic habitat for soil organisms Resist degradation
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  • Requirements good soil structure to provide adequate aeration (oxygen for respiration) good water infiltration (movement of water into the soil), moderate pH ( ideally between 6.0 to 7.5), low salinity (dissolved salts in soil water) low levels of potentially toxic elements such as boron, manganese and aluminum. balanced fertility that provides adequate levels of macro and micronutrients that plants and microbes require.
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  • Goals of a sustainable fertility/soil management program To sustain good productivity and crop quality. Provide a balanced nutrient supply for the crop. Time seasonal nutrient availability to correspond with crop demand. Minimize disease/pest susceptibility. Build soil OM as a long term reserve of nutrients and to maintain good soil structure and habitat for soil organisms To sustain environmental quality. Maintain or improve soil quality Minimize off-farm impacts, for example: Avoid non-point source pollution via surface runoff, erosion & leaching. Prevent soil erosion and sedimentation of waterways. Close nutrient cycles as much as possible: within the field, the farm, or within a watershed, and even at regional and national scales.
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  • It all starts with the soil and understanding how nutrients cycle in agroecosystems.
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  • Soil Development and Agroecosystems Soils = Climate, Organisms, Relief, Parent Material, Time. Soils=clorpt Agroecosystems alter soil processes! Practices modify soil properties Farmers manage soil chemistry and fertility
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  • Processes in the Soil Profile Source: The Nature of Soils, Brady 1999 Additions Losses Translocations - movement Transformations chemical changes
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  • Soil Texture Soils can be separated into different particles size fractions, e.g. Sand 0.05 mm 2 mm Silt0.002 mm 0.05 mm Clay
  • Soil pH and Nutrients Source: Brady and Weil, 1996 Farmers try manage soil pH carefully because it: Affects plant growth affects nutrient availability For example, Nitrification (NH 4 + --> NO 3 -) can reduce soil pH. Many growers will add lime to increase pH.
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  • Soil Microbial Processes Decomposition of plant and animal material. Mobilize (release into the soil) and Immobilize (assimilate) nutrients. Create Soil Structure by providing the glue to hold aggregates together, and creating pore spaces for air and water movement.
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  • Constituents of Soil Organic Matter Source: Brady and Weil, 1996
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  • Soil food web
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  • Plant macro-nutrients C, H, O Basic constituents of organic material N Proteins, chlorophyll, enzymes etc Ca Cell walls, cellular signals P Energy transfer - ATP etc Mg Chlorophyll, enzymes, protein synthesis S Proteins Cl Light reaction, ionic balance, stomatal movements K Ionic balance, osmosis, enzyme activator Micronutrients Zn, Mo, B, Mn, Cu
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  • Nutrient deficiencies in Tomato
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  • Nutrient Cycles: How nutrients move through the environment
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  • Simple N-cycle
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  • Lightning, pollution INPUT LOSS COMPONENT
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  • Nitrogen cycle characteristics Inputs: fertilizer manures & other organic materials N 2 fixation atmospheric deposition Main stores: atmosphere N 2 gas soil OM (>90% soil N) Outputs/losses crop harvest denitrification leaching erosion volatilization
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  • Microbes rule!!!!!!
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  • Key microbial processes & N transformations Mineralization: organic N inorganic N (many forms) (ammonium, NH 4 + ) Immobilization: inorganic N Organic N (ammonium, NH 4 + ) (many forms) (nitrate NO 3 - ) Nitrification: ammonium nitrite nitrate Denitrification: nitrate gaseous forms - nitrogen oxides and N 2 gas Ammonia volatization: ammonium, NH 4 + ammonia gas NH 3 N 2 - Fixation: Conversion of N 2 gas into organic forms of N
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  • Root nodules on clover root N 2 fixation: organisms in symbiotic relationships e.g. rhizobium and legumes, frankia and coeanothus, alder free living organisms N 2 NH 4 +
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  • 1.Ammonia release from soils increases as pH increases 2.Denitrification increases in wet soils 3.Both processes increase in warm soils Gaseous N Losses
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  • Phosphorous cycle characteristics Inputs: fertilizer manures & other organic materials plant residue atmospheric deposition (small) weathering of rocks Main stores: soil minerals & rocks soil OM much smaller % of total soil P than for N Outputs/losses crop harvest erosion leaching only if soil P exceedingly high Soil chemistry and mineralogy rule! - with microbes playing a greater role in high OM soils
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  • Role of mycorrhizae in Plant P uptake Known to be critical in low P natural ecosystems Some crops are partly dependent on mycorrhizal fungi: citrus, grapes, avocados, and bananas, Others that benefit from having them include: melons, tomatoes, peppers, squash, corn, millet, sorghum. Benefit of mycorrhizae highest at low moderate P favored when P is more limiting than C supply, not favored when P less limiting than C supply Roots colonized by mycorrhizae reduce penetration by root-feeding nematodes pest cannot pierce the thick fungal network. Can also improve drought tolerance, soil aggregation and N nutrition
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  • Types of mycorrhizae VAM or vesicular-arbuscular found on diverse set of plants except many trees Ectomycorrhizae Typically on woody plants
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  • VAM spores vesicle arbuscule
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  • Ectomycorrhizae on beech tree roots Root covered with fungal sheath X-section showing sheath Hyphae of sheath
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  • Managing Nitrogen Issue of synchrony between N mineralization and crop demand Timing of release depends on Moisture, temperature Quality of organic material being added
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  • What controls net mineralization of N Balance of mineralization vs immobilization C:N ratio microbes need about 25x as much C as N to grow If C:N ratio of organic amendment is immobilization If C:N ratio is around 25, then ---mineralization = immobilization If C:N ratio is >25 then N limits growth so microbes scavenge nitrogen --- mineralization


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