SOIL TEMPERATURE REGULATES PHOSPHORUS LOSS FROM LYSIMETERS FOLLOWING FALL AND WINTER MANURE APPLICATION

Applying manure in the fall and winter increases the potential for nutrient loss prior to crop uptake in the spring. In order to minimize the risk of nutrient loss, recommendations are often based on soil temperature, since biological activity has been shown to decrease substantially at temperatures less than 10 degrees C. These recommendations are often targeted toward reducing nitrogen (79 losses; thus, a smaller body of information is available on the fate of phosphorus (P) from fall and winter applied manure. The objective of this research was to determine how soil temperature affects P loss in runoff and leachate, and assess ovenvinter P losses based on application date and soil temperature. Nitrogen losses are discussed in a separate article. Dairy manure was surface applied to a channel); silt loam soil contained in lysimeters at soil temperatures of 15.7 degrees C, 4.8 degrees C, and -1.1 degrees C, which represented early fall, late fall, and winter applications, respectively. Phosphorus losses were determined during a series of rainfall simulations and natural precipitation events from October 2009 through March 2010. Phosphorus losses were significantly influenced by the soil temperature at the time of manure application and first rainfall-runoff event. As the soil temperature decreased, losses of DRP, TDP, and total P increased. Overwinter losses were also significantly impacted by soil temperature. The winter treatment had two times higher total P losses compared to the manure applied during the early fall. Results of this research show that soil temperature is important for determining P losses and that incorporating quantitative tools, such as soil temperature, into manure management plans could enhance P retention and help reduce the risk of overwinter P losses.