Runoff water quality characteristics following swine slurry application under broadcast and injected conditions

This study was conducted to measure the effects of swine slurry application method, time following slurry application, and runoff rate on selected water quality characteristics. Slurry from a commercial swine operation was broadcast or injected on field plots at a rate required to meet annual nitrogen requirements for corn. Rainfall simulation tests were conducted at five varying periods following slurry application. During each study period, three simulated rainfall events, separated by 24 h intervals, were applied for 30 min duration at an intensity of approximately 70 mm h^-1. Following the third rainfall simulation event, inflow was applied at the top of the plots in four successive increments to simulate greater plot lengths. Runoff samples were collected for analyses of dissolved P (DP), particulate P, total P (TP), NO₃-N, NH₄-N, total N, electrical conductivity, pH, and soil loss. The DP and TP loads of 0.35 and 0.46 kg ha^-1 measured for the broadcast treatment were significantly greater than the 0.13 and 0.19 kg ha^-1 obtained for the injection treatment. As time following slurry application increased from 1 to 3 days to 43 to 45 days, DP, TP, and NH₄-N loads decreased from 0.35 to 0.14, from 0.52 to 0.18, and from 2.17 to 0.14 kg ha^-1, respectively. Runoff rate significantly affected each of the measured water quality parameters. Runoff loads of DP, TP, and NH₄-N increased from 10.1 to 29.8, from 12.9 to 35.5, and from 13.9 to 25.1 g ha^-1 min^-1, respectively, as overland flow rate increased from 2.3 to 12.6 L min^-1. Application method, time following slurry application, and runoff rate are important variables influencing water quality characteristics of runoff.