Phosphorus Nelson

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Phosphorus Sources and Management in Organic Production Systems : 

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

Is P Fertility Inherently Different in Organic Agriculture?: 

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.

Is P Fertility Inherently Different in Organic Agriculture?: 

Is P Fertility Inherently Different in Organic Agriculture?

Is P Fertility Inherently Different in Organic Agriculture?: 

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

Arbuscular Mycorrhizal Fungi (AMF): 

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 respond to P additions (Dann et al., 1996). Credit: Randy Molina, Oregon State University, Corvallis

Is P Fertility Inherently Different in Organic Agriculture?: 

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 

N Source Effects on P Management – Feast or Famine: 

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

Phosphorus Sources for Organic Agriculture: 

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

Rock Phosphate as a P Source: 

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 phosphate mine in India

Rock Phosphate as a P Source: 

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

Rock Phosphate as a P Source: 

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

Rock Phosphate as a P Source: 

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

Green Manures as a P Source - ?: 

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

Green Manures as a P Source - ?: 

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

Manures and Composts as P Sources: 

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.

P Availability in Manures and Compost: 

P Availability in Manures and Compost P availability ranges from 70 to 100 % available. Use 70% for low P soils Use 100% for high P soils or maintenance applications Source: Sikora and Enkiri, 2005 Agron. J. 97:668-673.

P Availability in Manures and Compost: 

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

When P is in Excess: 

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

When P is in Excess: 

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)

When P is in Excess: 

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

When P in in Excess: 

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

Best Management Practices to Reduce P Losses: 

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.

In Summary…: 

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