Runoff Losses of N and P After Low Phosphorus Swine Slurry Application to No-Tillage Sorghum

Swine (Sus scrofa) manure can serve as a fertilizer source for crop production, but it typically contains more P relative to N than the crop requires, creating the potential for P losses in runoff. A 3-year study was conducted to compare runoff losses of NO3-N, NH4-N, total N, dissolved P, and total P under natural rainfall conditions from no-tillage sorghum plots [Sorghum bicolor (L.) Moench] receiving inorganic fertilizer, manure from swine fed low-phytate corn (Zea mays L.) diet, or manure from swine fed a traditional corn diet. Runoff (26.5 mm in 1999, 14.2 mm in 2000, and 1.6 mm in 2001), sediment loss (2.9 kg ha−1 in 1999, 0.9 kg ha−1 in 2000, and 0.4 kg ha−1 in 2001), and runoff nutrient losses differed among years but were similar among treatments within a year. Runoff losses of NO3-N (5.3 g ha−1 in 1999, 1.0 g ha−1 in 2000, and 2.6 g ha−1 in 2001), NH4-N (2.9 g ha−1 in 1999, 0.6 g ha−1 in 2000, and 5.6 g ha−1 in 2001), total N (89.7 g ha−1 in 1999, 8.4 g ha−1 in 2000, and 100.2 g ha−1 in 2001), dissolved P (1.5 g ha−1 in 1999, 0.5 g ha−1 in 2000, and 3.1 g ha−1 in 2001), and total P (3.8 g ha−1 in 1999, 0.9 g ha−1 in 2000, and 3.5 g ha−1 in 2001) from these plots represented less than 1% of that applied each year. Although use of low-phytate corn reduces manure P content, it did not decrease runoff P under these no-tillage conditions.