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.

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

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.

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.

It all starts with the soil and understanding how nutrients cycle in agroecosystems.

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

Processes in the Soil Profile Source: The Nature of Soils, Brady 1999 Additions Losses Translocations - movement Transformations chemical changes

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<0.002 mm Soils are a mixture of different soil particle sizes.

Soil Physical Properties Texture--particle size distribution. Structure--aggregate properties. Tilth--porosity and workability.

Soil Chemistry and Fertility Soil pH Cation exchange capacity (CEC) Organic Matter Nutrient availability

Cation Exchange Capacity Source: Brady and Weil, 1996 In many soils, mineral particles are negatively charged, which repel negatively charged ions (anions) and attract positively charged ions (cations).

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 > NO 3 -) can reduce soil pH. Many growers will add lime to increase pH.

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.

Constituents of Soil Organic Matter Source: Brady and Weil, 1996

Soil food web

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

Nutrient deficiencies in Tomato

Nutrient Cycles: How nutrients move through the environment

Simple N-cycle

Lightning, pollution INPUT LOSS COMPONENT

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

Microbes rule!!!!!!

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

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 +

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

INPUTLOSS COMPONENT

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

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

Types of mycorrhizae VAM or vesicular-arbuscular – found on diverse set of plants except many trees Ectomycorrhizae Typically on woody plants

VAM spores vesicle arbuscule

Ectomycorrhizae on beech tree roots Root covered with fungal sheath X-section showing sheath Hyphae of sheath

Managing Nitrogen Issue of synchrony between N mineralization and crop demand Timing of release depends on  Moisture, temperature  Quality of organic material being added

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<immobilization  Presence of resistant or inhibitory compounds slows mineralization  Lignin, polyphenols etc.

FIELD NITROGEN BALANCE Inputs = Imported fertilizer + atmospheric deposition + N 2 fixation Outputs = N exported in crop + N leached into ground water + N in eroded material + N lost by denitrification.

CASFS Farm Nitrogen Budget

% N%P%K Compost Compost Inputs 1 Inputs 2 Atmospheric deposition: Less than 1.0 kg/ha/year, of N, P and K, according to EPA data. Inputs 3 Biological nitrogen fixation – legumes hard to measure – major source of uncertainty in budget

OUTPUTS 1.Leaching – likely to occur in the fall and spring (difficult to measure) 2.Gaseous losses – quantitatively unlikely to be an important component. 3.Erosion – unlikely – CASFS farm fields generate little runoff.

SOM Soil solution

Fields studied Apples Tipi Pears Potatoes Strawberries Plums Main Field Onions+Garlic Mixed vegetables Ryegrass CSA Corn+Beans Mixed vegetables Garden

Main North Field – 1 year budget * 1/6 of amount applied every 6 years

Simulated budget for one rotation cycle

1.Biological N fixation (BNF) is crucial to compensate for the N exports. Cover crops need to fix 52 kg N/ha/year. 2.Do not know how much N lost by leaching 3.Estimation of BNF is needed to allow us to get an estimate of losses (leaching + gaseous) 4. Potassium export is exceeding input - use higher K compost or other sources of K 5. Phosphorus appears to be in balance Conclusions

Combine information from budgets with soil testing to refine fertility management