Organic fertility management

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.

2. 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

3. 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.

4. 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.

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

6. 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

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

8. Soil Texture • Soils can be separated into different particles size fractions, e.g. • Sand0.05 mm – 2 mm • Silt 0.002 mm – 0.05 mm • Clay <0.002 mm • Soils are a mixture of different soil particle sizes.

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

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

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

12. Soil pH and Nutrients • Farmers try manage soil pH carefully because it: • Affects plant growth • affects nutrient availability • For example, Nitrification (NH4+ --> NO3-) can reduce soil pH. Many growers will add lime to increase pH. Source: Brady and Weil, 1996

13. 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.

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

17. Soil food web

18. Plant macro-nutrients • C, H, OBasic 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

19. Nutrient deficiencies in Tomato

20. Nutrient Cycles:How nutrients move through the environment

21. Simple N-cycle

22. COMPONENT INPUT LOSS Lightning, pollution

23. Inputs: fertilizer manures & other organic materials N2 fixation atmospheric deposition Main stores: atmosphere N2 gas soil OM (>90% soil N) Outputs/losses crop harvest denitrification leaching erosion volatilization Nitrogen cycle characteristics

24. Microbes rule!!!!!!

25. Key microbial processes & N transformations • Mineralization: • organic N  inorganic N • (many forms) (ammonium, NH4+) • Immobilization: • inorganic N  Organic N • (ammonium, NH4+) (many forms) • (nitrate NO3-) • Nitrification: • ammonium  nitrite  nitrate • Denitrification: • nitrate  gaseous forms - nitrogen oxides and N2 gas • Ammonia volatization: • ammonium, NH4+  ammonia gas NH3 • N2 - Fixation: • Conversion of N2 gas into organic forms of N

26. Root nodules on clover root • N2 fixation: • organisms in symbiotic relationships e.g. rhizobium and legumes,frankia and coeanothus, alder • free living organisms • N2 NH4+

27. Gaseous N Losses • Ammonia release from soils increases as pH increases • Denitrification increases in wet soils • Both processes increase in warm soils

28. COMPONENT INPUT LOSS

29. 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 Phosphorous cycle characteristics

30. 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

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

32. VAM spores vesicle arbuscule

33. Ectomycorrhizae on beech tree roots Root covered withfungal sheath Hyphae of sheath X-section showing sheath

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

35. 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 <20-25, then excess N is released, ---mineralization>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.

37. FIELD NITROGEN BALANCE Inputs = Imported fertilizer + atmospheric deposition + N2fixation Outputs = N exported in crop + N leached into ground water + N in eroded material + N lost by denitrification.

39. CASFS Farm Nitrogen Budget

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

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

42. Atmospheric deposition Gaseous loss Nitrogen fixation Compost Products SOM Cover crops Soil solution Runoff Unnacounted for Leaching

43. Fields studied Onions+Garlic Mixed vegetables Ryegrass CSA Corn+Beans Apples Plums MainField Pears Tipi Strawberries Potatoes Garden Mixedvegetables

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

45. Simulated budget for one rotation cycle

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

47. Combine information from budgets with soil testing to refine fertility management