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Title: SOIL INVERSION BY PLOWING DECREASES SURFACE SOIL AND RUNOFF PHOSPHORUS

Author
item Sharpley, Andrew

Submitted to: American Society of Agronomy Monograph Series
Publication Type: Other
Publication Acceptance Date: 7/23/2003
Publication Date: 11/4/2003
Citation: Sharpley, A.N. 2003. Soil inversion by plowing decreases surface soil and runoff phosphorus[abstract]. American Society of Agronomy Abstracts. Paper #903014

Interpretive Summary: Not applicable.

Technical Abstract: The application of fertilizer and/or manures year after year to the same field can increase the amounts of phosphorus in soil to levels that are well above those needed by crops to grow. In many soils, most of this added phosphorus occurs at the top or surface of the soil, where it is vulnerable to removal by surface runoff during heavy rains. The phosphorus may then be transported by rivers and streams to lakes, which can accelerate freshwater eutrophication. Eutrophication restricts water use for fisheries, recreation, industry, and drinking, due to the increased growth of undesirable algae and aquatic weeds. Death and decomposition of these aquatic plants causes oxygen shortages. With the advent of new nutrient management regulations, farmers would not be able to apply any more phosphorus to these soils. In areas where there are high numbers of animal feeding operations, this restriction could severely limit options for land applying manures. A study to see if plowing soils with high levels of phosphorus could decrease levels at the surface, thereby decreasing the potential for phosphorus loss in runoff and giving farmers another option when implementing Comprehensive Nutrient Management Planning strategies, is published in the July/August issue of "Journal of Environmental Quality." This research was conducted in 2000 to 2001 at sites that had received either dairy, poultry, or swine manure for up to 20 years. Study sites have soil test phosphorus levels in the surface 5 cm of the soil profile that are at least three times crop needs. The author showed by laboratory experiments that high plant-available phosphorus levels in surface soil was decreased when mixed with low phosphorus subsoil. This was attributed to dilution effects as well as the sorption of phosphorus by clays in the subsoil. When one of these phosphorus-stratified soils in central Pennsylvania was moldboard plowed to about 20 cm and planted orchardgrass had become established, concentrations of dissolved and sediment-bound phosphorus in runoff were reduced 10- and 3-fold, respectively. Andrew Sharpley stated, 'This research demonstrated that the one-time plowing of soils with high levels of phosphorus at the surface has the potential to decrease phosphorus loss in surface runoff, as long as erosion is minimized after plowing by the immediate 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 additional management options under phosphorus-based nutrient management strategies.