Soil Mixing to Decrease Surface Stratification of Phosphorus in Manured Soils

Continual applications of fertilizer and manure to permanent grassland or no-till soils can lead to an accumulation of P at the surface, which in turn increases the potential for P loss in overland flow. To investigate the feasibility of redistributing surface stratified P within the soil profile by plowing, Mehlich-3 P rich surface soils (128–961 mg kg-1 in 0–5 cm) were incubated with lower-P subsoil (16–119 mg kg-1 in 5–20 cm) for 18 manured soils from Oklahoma and Pennsylvania that had received long-term manure applications (60–150 kg P ha-1 yr-1 as dairy, poultry, or swine manure for up to 20 yr). After incubating a mixture of 5 g surface soil (0- to 5-cm depth) and 15 g subsoil (5- to 20-cm depth) for 28 d, Mehlich-3 P decreased 66 to 90% as a function of the weighted mean Mehlich-3 P of surface and subsoil (i.e., 1:3 ratio) (r2 = 0.87). At Klingerstown, Northumberland County, south central Pennsylvania, a P-stratified Berks soil (Typic Dystrochrept) (495 mg kg-1 Mehlich-3 P in 0to 5-cm depth) was chisel plowed to about 25 cm and orchardgrass (Dactylis glomerata L.) planted. Once grass was established and erosion minimized (about 20 wk after plowing and planting), total P concentration in overland flow during a 30-min rainfall (6.5 cm h-1) was 1.79 mg L-1 compared with 3.4 mg L-1 before plowing, with dissolved P reduced from 2.9 to 0.3 mg L-1. Plowing P-stratified soils has the potential to decrease P loss in overland flow, as long as plowing-induced erosion is minimized.