Soil, topography, and climate influence how changes in tillage or manure application increase or decrease runoff P losses. Shown below are graphs of comparing P Index loads for ten fields with three different managements. All of the fields have a soil test P of 70 ppm and have a rotation of three years of corn silage followed by four years of alfalfa. Liquid dairy manure was applied at 7,000 gallons per acre to the second year of corn , 14,000 gallons per acre before the third year of corn, and 14,000 gallons per acre before the alfalfa was seeded.
Management 1: Fall chisel plowing for corn and alfalfa seeding with manure incorporated by this tillage
Management 2: No-till all years with manure surface-applied in fall
Management 3: No-till all years with 7,000 gallons per acre manure applied in winter, remainder in fall
As you can see, the P Index values vary a lot from field to field under the same managements. Site susceptibility to erosion and runoff influence P losses. For these fields, the comparatively steep and erodible Ashdale silt loam in Green County has the highest particulate P loads for all managments. The Pella silt loam has a high potential for rainfall runoff, and therefore has the highest soluble P losses for no-till. Soluble P Index loads from manure applications increase for all fields when manure is applied in the winter insead of the fall.
Click on the individual graphs to get more details. Use the arrows on your keyboard to move through the graphs. Press esc on your keyboard to exit out of the images.