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) ( r 2 = 0.87). At Klingerstown, Northumberland County, south central Pennsylvania, a P‐stratified Berks soil (Typic Dystrochrept) (495 mg kg −1 Mehlich‐3 P in 0‐ to 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.