Phosphorus Index Based Management Douglas Beegle Dept. of Crop and Soil Sciences Penn State University

Why do we need a P Index? Why not just agronomic recommendations? NP2O5P2O5 K2OK2O Nitrogen Based Corn/Dairy Manure Regional P Balance ¼ ¾ Manure Crops Soil Animals Feed Eutrophication Nutrient flows in modern ag P Index ? Field P Balance NP2O5P2O5 K2OK2O Phosphorus Based Corn/Dairy Manure P Index

SourceTransport Critical Source Area P Index Critical Source Area Management Overlap of Source & Transport Indicators Identify and manage the critical source areas Evaluate environmental risk Target effort and resources

Critical Areas of P Export 90% of annual P export comes from 10% of land area Mahantango Creek Watershed, USDA-ARS 90% of P Loss comes from 10% of the watershed

Managing Phosphorus Pollution Subsurface flow Tile flow Leaching Sources Transport Erosion Runoff N P K Hydrology Water Body

Mehlich-3 soil P, mg/kg P loss, lb P 2 O 5 /A Soil Test vs P Loss R 2 = Sharpley, USDA-ARS Crop P Optimum P Threshold No recent P inputs

Managing Phosphorus Pollution Subsurface flow Tile flow Leaching Sources Transport Erosion Runoff Hydrology Water Body N P K

Mehlich-3 soil P, mg/kg P loss, lb P 2 O 5 /A 75 kg P/ha TSP 112 kg P/ha swine slurry 150 kg P/ha poultry manure 75 kg P/ha TSP 112 kg P/ha swine slurry 150 kg P/ha poultry manure Soil Test vs P Loss - with applied P Soil Only R 2 =0.80 For all data points R 2 = Sharpley, USDA-ARS

Phosphorus Index P Source Site Characteristics –Environmental Soil Test P Same soil test different interpretation Sampling Questions? P Saturation? –P Fertilizer Rate and Appl. Method –Organic P Rate and Appl. Method P Source Coefficient (PSC) –Direct availability of manure P to runoff –Based on WEP in manure

Managing Phosphorus Pollution Subsurface flow Tile flow Leaching Sources Transport Runoff N P K Hydrology Water Body Erosion

Phosphorus Transport by Erosion Erosion reduced 95% Conventional till wheat Converted to no-till Total P mg/L Sharpley, USDA-ARS

Managing Phosphorus Pollution Subsurface flow Tile flow Leaching Sources Transport Erosion N P K Hydrology Water Body Runoff

Zone of Interaction with Runoff Mehlich 1 P (mg/kg) Depth (cm) Data from Mozaffari and Sims, 1994 Zone of interaction with runoff Plow depth  Location of applied P  Interaction with runoff P on surface Soil test at surface High P Saturation at surface P sat = P / Al + Fe Oxalate extr. or Mehlich 3 extr.

Soluble P Transport in Runoff Conventional till wheat Algal-available P, mg/L Converted to no-till Sharpley, USDA-ARS

Managing Phosphorus Pollution Subsurface flow Tile flow Sources Transport Erosion Runoff N P K Hydrology Water Body Leaching

Soluble P Loss by Sub-surface flow Very Dependent on soil properties –Hydrology Piston flow Macro pores –Texture –Soil Chemistry (Fe, Al, Ca) –P loading/saturation –Artificial Drainage Data from: Bolton et al., 1970 Culley and Bolton, 1983

P Loss is a Complex “Landscape” Process Subsurface flow Tile flow Leaching Sources Transport Erosion Runoff N P K Hydrology Water Body

Modified Connectivity: Direct Connection Landscape Transport Modified Connectivity: Riparian Buffer Distance Runoff Return Period Hydrology

Phosphorus Index P Transport Site Characteristics –Soil Erosion –Runoff Class –Leaching Potential Sub-surface Drainage –Contributing Distance –Modified Connectivity Erosion Runoff Drainage Distance

PA Phosphorus Index v 2.0

P loss, kg/ha P index value for the site kg P/ha TSP 112 kg P/ha swine slurry 150 kg P/ha poultry manure 75 kg P/ha TSP 112 kg P/ha swine slurry 150 kg P/ha poultry manure P Index describes P loss potential Very high High MediumLow Sharpley, USDA-ARS R 2 =0.79

Phosphorus Index Low P Index –N Based Management Medium P Index –N Based Management High P Index* –P Based: Crop removal Very High P Index* –No P: Manure or Fertilizer High and Very High* –Modify Management based on P No or reduced manure Change time or method of application Conservation practices Buffers Etc.

Phosphorus Nutrient Management Plan Develop N based plan –Usually means excess P will be applied Use P Index to evaluate the N based plan –Is the risk of P loss acceptable Acceptable risk N rate, excess P Unacceptable Risk –Modify N based plan, where necessary, to address P loss risk NP2O5P2O5 K2OK2O Nitrogen Based Corn/Dairy Manure NP2O5P2O5 K2OK2O Phosphorus Based Corn/Dairy Manure or

P Index Application Eventually, all fields will have a high P index P Index is not the solution –Tool to buy time to solve problem –Minimizes negative impact of P while we come up with a sustainable solution –We need to get the system into better balance

NRCS/EPA P Index Issues Proposed change in NRCS 590 Std. –P soil test only – No more P Index Easy to regulate Very strict limits Not supported by the science - Source/Transport Unrealistic for animal agriculture to comply with in short term Better soil P balance is a good long term goal –Withdrawn, under further review

College of Agricultural Sciences Department of Crop and Soil Sciences