Author
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Sharpley, Andrew |
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Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 8/7/2002 Publication Date: 7/3/2003 Citation: SHARPLEY, A.N. SOIL MIXING TO REDUCE SURFACE STRATIFICATION OF PHOSPHORUS IN MANURED SOILS. JOURNAL OF ENVIRONMENTAL QUALITY. 2003. V. 32. P. 1375-1384. Interpretive Summary: The application of fertilizer and / or manures year after year to the same field, can increase the amounts of phosphorus in soil to levels which are well above those needed by crops to grow. In many soils, most of this phosphorus increase occurs at the top or surface of the soil and is very vulnerable to be removed during heavy rainfalls, when surface runoff occurs. This phosphorus is then transported by rivers and stream to lakes, causing a decrease in water quality. With the advent of new nutrient management regulations, farmers would not be able to apply any more phosphorus to these soils and in areas where there are high numbers of animal feeding operations, and this could severely limit their options for applying manures. Thus, we conducted a study to see if plowing these high phosphorus soils could decrease levels at the surface, thereby decreasing the potential for phosphorus loss in runoff, and enable farmers to possibly apply manure. The combined laboratory incubation and field study, demonstrated the potential benefits of a one-time plowing of soils with high levels of phosphorus at the surface, as long as erosion was minimized after plowing by the rapid establishment of a plant cover that protects the soil surface. Overall, plowing these soils may reduce the long-term loss of phosphorus in surface runoff and provide farmers an additional option in keeping these soils in production under phosphorus-based nutrient management strategies. Technical Abstract: Continual applications of fertilizer and manure can lead to an accumulation of P at the soil 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 to 961 mg/kg in 0 to 5 cm) were incubated with P-deficient subsoil (16 to 119 mg/kg in 5 to 20 cm) for 18 manured soils from Oklahoma and Pennsylvania that had received long-term manure applications (60 to 150 kg P/ha/yr as dairy, poultry, or swine manure for up to 20 years). 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 days, Mehlich-3 P decreased 66 to 90 % as a function of subsoil clay (r2 of 0.84). At Klingerstown, Northumberland Co., south central PA, a P-stratified Berks soil (495 mg/kg Mehlich-3 P in 0- to 5-cm depth) was moldboard plowed to about 20 cm and Orchardgrass (Dactylis glomerata L.) planted. Once grass was established and erosion minimized (about 20 weeks after plowing and planting), total P concentration in overland flow during a 30-min rainfall (6.5 cm/hr) was 1.79 mg/L compared to 3.4 mg/L prior to plowing, with dissolved P reduced from 2.9 to 0.3 mg/L. The one-time plowing of P-stratified soils has the potential to decrease P loss in overland flow, as long as plowing-induced erosion is minimized by the immediate establishment of a protective vegetative ground cover. |
