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Phosphorus Sources and Management in Organic Production Systems

Phosphorus Sources and Management in Organic Production Systems . Nathan O. Nelson 1 and Rhonda Janke 2 1 Kansas State University Department of Agronomy 2 Kansas State University Department of Horticulture, Forestry, and Recreation Resources.

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Phosphorus Sources and Management in Organic Production Systems

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  1. Phosphorus Sources and Management in Organic Production Systems Nathan O. Nelson1 and Rhonda Janke2 1Kansas State University Department of Agronomy 2Kansas State University Department of Horticulture, Forestry, and Recreation Resources

  2. Is P Fertility Inherently Different in Organic Agriculture? • “The aim of nutrient management within organic farming systems is to work, as far as possible, within a closed system” Stockdale et al., 2001. • “Dependence on external inputs, whether chemical or organic, is reduced as far as possible.” Elmaz et al., 2004. • “Organic farming systems rely on the management of soil organic matter to enhance the chemical, biological, and physical properties of the soil, in order to optimize crop production.” Watson et al., 2002.

  3. Is P Fertility Inherently Different in Organic Agriculture?

  4. Is P Fertility Inherently Different in Organic Agriculture? • Organically produced crops still need P • Soil properties affected by management/ cropping systems can alter P availability and cycling • Arbuscular mycorrizal fungi • Organic carbon

  5. Arbuscular Mycorrhizal Fungi (AMF) • Symbiotic association between fungus and root • Root provides food (carbon source) • Fungus increases root exploration and nutrient uptake. • Organic Agriculture tends to increase AMF • Will sometimes increase P uptake/crop growth (Kahiluoto and Vestberg, 1998). • …and sometimes not (Scullion et al., 1998) • Even with AMF, organically grown crops still respondto P additions (Dann et al., 1996). Credit: Randy Molina, Oregon State University, Corvallis

  6. Is P Fertility Inherently Different in Organic Agriculture? • Organically produced crops still need P • Soil properties affected by management/ cropping systems can alter P availability and cycling • Arbuscular mycorrizal fungi • Organic carbon • Organic production does not produce consistent effects for these properties/processes • Other agricultural practices will increase OC and positively affect AMF. • Phosphorus Sources 

  7. N Source Effects on P Management – Feast or Famine • Fresh plant biomass has N:P ratio of ~ 8:1 • Organic N sources supplying ample P • Manures – dairy, beef, swine, poultry litter (~4:1) • Composted manures – increases P concentration (~2:1) • Plant composts – N:P varies • Avg. 6:1with a high 11:1 and low of 1:1 • Organic N sources supplying little or no P • Green Manures • Blood Meal

  8. Phosphorus Sources for Organic Agriculture • Inorganic P Sources • Rock Phosphate • Bone Meal • Organic-based P sources • Green Manures - ? • Manures • Composts • Composted Manures • Composted Plant Biomass

  9. Rock Phosphate as a P Source • Rock phosphate (RP) is a slowly soluble P source from mined phosphate (calcium phosphates). • Solubility is highly dependant on several factors • Soil type • Low pH • Low Ca • Low P fixing Capacity • RP source • Sedimentary RP Reactive/soft (North Carolina, Gafsa) • Igneous and Metamorphic Rock phosphatemine in India

  10. Rock Phosphate as a P Source • Phosphorus availability – relative response approaches 1:1 • Optimum soiland RP source Source: Correa et al., 2005.Sci. Agric. 62:159-164

  11. Rock Phosphate as a P Source • Phosphorus availability – relative response does not approach 1:1 • 6-yr field study • Low pH soil • Lime applicationbefore year 1 Source: Scholefield et al., 1999Nutr. Cycl. Agroecosyst. 53:147-155

  12. Rock Phosphate as a P Source • Green manures can increase RP efficacy • 200 kg P ha-1 Source: Zaharah and Bah. 1997. Nutr. Cycl. Agroecosyst. 48:247-255

  13. Green Manures as a P Source - ? • Green Manures – legume crops grown and tilled in to soil (not harvested). • Some species can extract soil P that is unavailable to other crops (e.g., white lupin, faba bean, nitro alfalfa). • Decomposition releases P • Some green manures may decrease P uptake of succeeding crop (e.g., white lupin). • Green manures may increase P availability, but are not a P source

  14. Green Manures as a P Source - ? Change in Soil Test P during Green manure – Sorghum rotationSource: Cavigelli and Thien, 2003. Soil Sci. Soc. Am. J. 76:1186-1194 5 4 2 3 1 “…[green manures] cannot substitute for maintenance Pfertilizer application.” (Horst et al., 2001)

  15. Manures and Composts as P Sources • Majority of P in manures and composts is inorganic P Source: Eghball et al., 2002. J. Soil Water Conserv. 57:470-473.

  16. P Availability in Manures and Compost • P availability ranges from 70 to 100 % available. • Use 70% forlow P soils • Use 100% forhigh P soils ormaintenance applications Source: Sikora and Enkiri, 2005Agron. J. 97:668-673.

  17. P Availability in Manures and Compost • High variability between manure types Changes in Mehlich 3 P for 80 d followingapplication of 4 manures and fertilizer Relationship between the C/P ratioand the Olsen P in three soils Source: Griffin et al., 2003Soil Sci. Soc. Am. J. 67:645-653. Source: Leytem et al., 2005. Soil Sci. Soc. Amer. J. 69:1516-1524.

  18. When P is in Excess • P inputs to surface waters promote eutrophication and degrade water quality

  19. When P is in Excess • Continual use of Manures and composts to supply N can increase soil test P far beyond crop requirements • Organic farming with poultry litter as the sole N source raised soil test P to 800 to 1000 mg P kg-1 (Mikkelsen, 2000)

  20. When P is in Excess • High soil test P results in higher runoff Plosses. Source: Tarkelson and Mikkelsen, 2004Comm. Soil Sci. Plant Anal. 35:2987-3007.

  21. When P in in Excess • Surface application ofbroiler litter resulted inhigh runoff P concn.regardless of soil Pconcentration. • High litter rate = 200kg N ha-1 Source: Tarkelson and Mikkelsen, 2004J. Environ. Qual. 33:1424–1430.

  22. Best Management Practices to Reduce P Losses • No-till/Cover Crops • Reduces runoff volume and erosion • Grass Buffer Strips • Trap sediment and increase infiltration • Incorporation of manure/compost prior to rainfall • Reduces interaction of manure/compost with runoff water.

  23. In Summary… • Inorganic P Sources • Rock Phosphate – only acidic soils • Bone Meal – acidic soils • Organic-based P sources • Manures – good P source 70-100% available • Composts • Composted Manures – similar to manures • Composted Plant Biomass – higher C:P ratio, may be less available than other composts • Use BMPs to reduce erosion and runoff when applying manures and composts

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