My Field has High Soil Test P. Now what? John A. Lory, Ph.D. Division of Plant Sciences Commercial Agriculture Program University of Missouri

Nutrient Management Scale Farm P Assessment Scale Field

Water Quality Scale Watershed

Water Quality Scale Watershed Nutrient Management Scale Farm P Assessment Scale Field

Lake 3 – MU Dairy Farm Lake: 6 acres Watershed: 77 acres Mean soil test P: 94 lbs/a 197 ppb P

Missouri Reservoirs Jones and Knowlton 1993 Water Clarity as measured by Secchi depth (m) Missouri reservoirs Lake 3

Lake 1 – MU Dairy Farm Lake: 15 acres Watershed: 135 acres Mean soil test P: 69 lbs/a 223 ppb P

Lake 2 – MU Dairy Farm Lake: 2.4 acres Watershed: 22 acres Mean soil test P: 91 lbs/a Lake 2 68 ppb P

Understanding Edge of field P losses

Bray-1 Soil Test P (lbs/acre) Dissolved Reactive P in runoff (ppb) Effect of soil test P on runoff P in forage systems (small plot runoff) Creldon Soil

What are my options? 223 ppb P

What are my options? Improve timing of application 223 ppb P

Water Soluble P in Runoff (ppm) Days After Treatment 200 lbs./acre phosphate applied 3/22/00 to forages Mt. Vernon, MO Improve timing of surface application

Days after application Dissolved Reactive P (mg kg -1 ) DAPPoultry Litter Effect of recently applied P on runoff P in forage systems

Aug.Oct. Nov. Dec.Jan. Volumetric Water Content (%) Soil moisture at Mt. Vernon, MO 2003 Saturated soil Feb.Mar.Apr.MayJun.Jul.Sep. 2 inches 4 inches Precipitation (in)

Aug.Oct. Nov. Dec.Jan. Volumetric Water Content (%) Soil moisture at Mt. Vernon, MO 2004 Saturated soil Feb.Mar.Apr.MayJun.Jul.Sep. 2 inches 4 inches Precipitation (in)

Nitrogen for Tall Fescue Hay AprilAugustOctoberJune Forage yield Herd feed requirement

Litter is an excellent fertilizer for fall fescue growth

What are my options? Lower P index on fields 223 ppb P

The importance of erosion TreatmentSTP Soluble P in runoff Erosion Runoff volume ppm kg/hamm Pasture Tillage w/residue Tillage w/o residue

What are my options? Lower P balance watershed 223 ppb P Export more manure Import less manure and fertilizer

What are my options? Lower P balance watershed 223 ppb P Should I raise STP on this field?

Raise soil test P 10 units with manure Low testing field: 5 ppm to 15 ppm Very high testing field: 50 to 60 ppm Very high testing field: 500 to 510 ppm Is there a water quality benefit from choosing one field over another?

Raise soil test P 10 units with manure Low testing field: 5 ppm to 15 ppm –Improved yield and forage quality –Reduced erosion –Lower runoff volume Very high testing field: 50 to 60 ppm Very high testing field: 500 to 510 ppm

What are my options? Follow the rules. 223 ppb P No application on frozen or saturated soils No application on >10% slope Adhere to setback requirements

What are my options Improve timing of applications Lower field P index Import less and export more P Follow the rules

Some philosophy It is a lot easier to avoid a problem then to fix a problem. The P index is best used as a educational tool, not a justification for more manure applications