Soil Phosphorus Issues Miguel Cabrera and David Radcliffe Crop and Soil Sciences University of Georgia

Intended Outcomes Understand how P affects water quality Understand how P behaves in soil Understand why manures present a special problem with P Understand how to use the Phosphorus Index

How P Affects Water Quality High levels of nutrients cause accelerated eutrophication (algal blooms) P controls eutrophication in fresh water Lakes are more sensitive than streams Eutrophication can increase: aquatic weeds algal growth low oxygen levels, fish kills, bad-tasting water (geosmin)

Natural Process Accelerated by land use

Accelerated Eutrophication Lake in Canada Divided by plastic curtain For 8 years –Nitrogen added each year to one side –Nitrogen and phosphorus added to other side Every year there was an algal bloom in response to adding phosphorus sheries/eutro.html

How P Affects Water Quality High levels of nutrients cause accelerated eutrophication P controls eutrophication in fresh water Lakes are more sensitive than streams Eutrophication can increase: aquatic weeds algal growth low oxygen levels, fish kills, bad-tasting water (geosmin)

How P Affects Water Quality Summer 2007

Georgia Lakes with P TMDLs Lake Lanier (2006) Lake Allatoona (2006) Carters Lake (2006) Lake Walter F George (2006)

Intended Outcomes Understand how P affects water quality Understand how P behaves in soil Understand why manures present a special problem with P Understand how to use the Phosphorus Index

How P Behaves in Soil

Soil test P (ppm) Soil depth (inches) No manure 40 lb P/acre/yr 90 lb P/acre/yr 110 lb P/acre/yr

How P Behaves in Soil Mehlich-3 soil P (ppm) Dissolved P in surface runoff (ppm) Surface runoff

Intended Outcomes Understand how P affects water quality Understand how P behaves in soil Understand why manures present a special problem with P Understand how to use the Phosphorus Index

Why Manures Present a Problem Soil P levels high enough to cause runoff P concentrations > 1 ppm unlikely with fertilizer Cost discourages over-application of P Over-application of P occurs with manures N-to-P ratio in manures is not the same as what crops need

Why Manures Present a Problem Most crops need about 8 lbs available N for every lb of P N:P ratio of 8:1 In typical broiler litter there are about 35 lb of available N and 30 lb of P per ton of litter N:P = 1.2:1 For every 8 lb of N, litter supplies 6.7 lb of P 6.7 times as much P as crop needs

N:P Ratios in Manures Type of ManureAvailable N:P Ratio Over-application of P Anaerobic Swine Lagoon times crop needs Anaerobic Dairy Lagoon times crop needs Anaerobic Layer Lagoon times crop needs Broiler Litter times crop needs

Cycling of P: Before World War II

Cycling of P: After World War II Manure P P Rock Grain P Manure P

Regional Imbalance of P Typical poultry ration contains 60% corn Less than 10% of the corn used in Georgia poultry feed is produced in the state Georgia imports 135 million bushels of corn per year Nearly 8,000 tons P imported each year

Long-term Solution: Close the Loop One way to restore the P cycle would be to feed more locally-grown grain Return manure to these fields Expand acreage for manure application Corn acreages could be expanded But corn has problems with drought- tolerance, aflatoxin, and pests

Long-term Solution: Close the Loop New pearl millet hybrid may be a promising feed grain

Long-term Solution: Close the Loop New pearl millet hybrid is called “Tifgrain 102” Can be used as a substitute for corn grain in poultry, cattle, swine, and dairy rations Check with county agent about local markets htm

Short-term Solution: BMP’s Alter feed ration to reduce P in manure Add alum to waste water Don’t apply manure when runoff is likely Incorporate or inject manures Avoid artificially drained fields Grass filters and stream-side buffers Use practices that reduce runoff and erosion

Objectives Understand how P affects water quality Understand how P behaves in soil Understand why manures present a special problem with P Understand how to use the Phosphorus Index

Soluble P Particulate P Soluble P

Overall Structure Soluble Phosphorus in Surface Runoff Particulate Phosphorus in Surface Runoff Soluble Phosphorus in Leachate + + Phosphorus Index

Soluble Phosphorus in Surface Runoff STP Org. P Inorg. P DRP

Soluble Phosphorus in Surface Runoff Soil Test P mg P/L Organic P mg P/L Inorganic P mg P/L ++ X Runoff (L)

ManureWater Soluble Factor Poultry litter (with alum)0.15 Poultry litter (no alum)0.30 Layer manure0.40 Dairy manure0.65 Swine manure0.40 Layer slurry0.40 Dairy slurry0.65 Swine slurry0.25

Yearly Runoff Estimation

Soluble Phosphorus in Surface Runoff Soil Test P mg P/L Organic P mg P/L Inorganic P mg P/L ++ X Runoff X Buffer Effect

Effect of Buffer Width If STP < 450 BF = e ( Width) If STP > 450 BF = 1

Overall Structure Soluble Phosphorus in Surface Runoff Particulate Phosphorus in Surface Runoff Soluble Phosphorus in Leachate + + Phosphorus Index

BAP Particulate Phosphorus in Surface Runoff

Sediment Loss (RUSLE) (tons/ac/yr) Bioavailable P in sediment (mg/kg) Particulate Phosphorus in Surface Runoff x

Sediment Loss (RUSLE) (tons/ac/yr) Bioavailable P in sediment (mg/kg) X Buffer Effect Particulate Phosphorus in Surface Runoff x

Overall Structure Soluble Phosphorus in Surface Runoff Particulate Phosphorus in Surface Runoff Soluble Phosphorus in Leachate + + Phosphorus Index

STP Org. P Inorg. P DRP Soluble Phosphorus in Leachate DRP

Soil Test P mg P/L Organic P mg P/L Inorganic P mg P/L ++ X Leachate Volume Soluble Phosphorus in Leachate

Estimation of Leachate Volume Leachate Vol (mm) = (P - 0.4s) 2 /(P + 0.6s) x 25.4 P = Annual precipitation = 50 inches s = (1000/CN) – 10 CN = curve number for percolation Williams and Kissel (1991) Hydrologic GroupABCD CN for Percolation

Volume of Yearly Leachate 1250 mm rain

Soil Test P mg P/L Organic P mg P/L Inorganic P mg P/L ++ X Leachate Volume Soluble Phosphorus in Leachate Depth to Water Table Factor

Overall Structure Soluble Phosphorus in Surface Runoff Particulate Phosphorus in Surface Runoff Soluble Phosphorus in Leachate + + Phosphorus Index

How to Use the P-Index Use P Index (Excel spreadsheet) P index = Risk of soluble P in runoff + Risk of particulate P in runoff + Risk of soluble P in leachate

Phosphorus Index Inputs Phosphorus Sources Phosphorus Transport Best Mgmt. Practices (BMP’s)

P Index Input: P Sources Soil P (soil test P) Fertilizer P Manure P

P Index Inputs: Soil Test P Lab analysis: Mehlich 1 –UGA Soil Test Lab uses this method Other labs may use Mehlich 3 The two methods give different numbers and there is no good way to convert Mehlich 3 to Mehlich 1 Be sure your lab is using Mehlich 1 !

P Index Inputs: Manure P Soil test lab analysis of dry and liquid manure will give P 2 O 5 in lbs –Dry manure: lb per ton –Liquid manure: lb per acre-in or lbs per 1,000 gal If you don’t use lab analysis, P 2 O 5 content must be calculated –Example 1: Apply 5 ton of poultry manure/acre –Assume 1.5% P content for manure –1.5% x 2,000 lb = 30 lb P per ton –30 lb/ton x 5 ton/A x 2.29 = 344 lb P 2 O 5 per acre –2.29 conversion factor for converting P to P 2 0 5

P Index Inputs Summary Manure/Fertilizer information –Source, application method, and rate –From manure test reports: P 2 O 5 content Soil information –From soil test reports: STP –From county soil survey map: soil series (hydrologic group) and depth to water table –From NRCS office: curve number and erosion rate –Curve number can also be obtained from TR-55 using soil series and management

P Index Categories P index range CategoryInterpretation 0 to <40LowN-based NMP is usually satisfactory. 40 to <75MediumUse conservation practices and P applications that maintain a P Index < to <100HighAdd conservation practices or reduce P applications to achieve a P Index < or greater Very High Add conservation practices or reduce P applications to achieve a P Index < 100 in the short term. Develop a management plan with the goal of achieving a P Index < 75 within 5 years.

LOWMEDIUMHIGHV. HIGH

Example #12345 ManureBroiler CropPasture STP (lb/acre)450 P 2 O 5 (lb/acre)344 Manure methodDec-Feb Soil seriesCecil Curve #7075 Erosion (T/acre)0.1 Water table (ft)15 BMPsnone P index AlternativesTime of application or rate

Example #12345 ManureBroiler CropPasture Corn STP (lb/acre) P 2 O 5 (lb/acre) Manure methodDec-Feb <30 days Soil seriesCecil Curve # Erosion (T/acre) Water table (ft)15 3 BMPsnone P index AlternativesTime of application or rate OK

Example #12345 ManureBroiler CropPasture Corn STP (lb/acre) P 2 O 5 (lb/acre) Manure methodDec-Feb <30 days Soil seriesCecil Curve # Erosion (T/acre) Water table (ft)15 33 BMPsnone P index AlternativesTime of application or rate OKBuffer, time of application, or rate

Example #12345 ManureBroiler Dairy CropPasture Corn Pasture STP (lb/acre) P 2 O 5 (lb/acre) Manure methodDec-Feb <30 days Sprinkler Soil seriesCecil Curve # Erosion (T/acre) Water table (ft)15 33 BMPsnone None P index AlternativesTime of application or rate OKBuffer, time of application, or rate

Summary Excess P causes fresh water eutrophication Build up of soil test P leads to P in runoff Manures based on N supply too much P P imported in corn and soybean for rations Growing pearl millet may help close P loop P Index is used to assess risk of P loss Input: soil test P, fertilizer P, manure P Input: soil series, curve number, erosion loss BMP’s can be used to reduce P Index value

Reference Web Sites AWARE – aware/newtools.phpwww.engr.uga.edu/service/extension/agp2/ aware/newtools.php –P index calculator – Excel spreadsheet –P index documentation – pdf file NRCS – Q/H&H/Tools_Models/WinTR55.htmlhttp:// Q/H&H/Tools_Models/WinTR55.html –TR 55 for determining curve #’s