Runoff nutrient transport as affected by land application method, swine growth stage, and runoff rate

This study was conducted to measure the effects of slurry application method, swine growth stage, and flow rate on runoff nutrient transport. Swine slurry was obtained from production units containing grower pigs, finisher pigs, or sows and gilts. The swine slurry was applied using broadcast, disc, or injection methods at a rate required to meet annual nitrogen requirements for corn. Three 30 minute simulated rainfall events, separated by 24 hour intervals, were applied to the experimental plots at an intensity of 70 mm hr ^-1. Inflow was applied at the top of each plot in four successive increments after the third rainfall simulation run to simulate greater plot lengths. The dissolved phosphorus (DP) load of 0.20 kg ha^-1 obtained on the broadcast treatment was significantly greater than the 0.11 and 0.08 kg ha^-1 measured on the disc and injected treatments, respectively. The DP runoff load of 0.17 kg ha^-1 measured for the sows and gilts treatment was significantly greater than the 0.11 kg ha^-1 obtained for the finisher treatment. In contrast, the NH₄-N load of 0.70 kg ha^-1 obtained on the finisher treatment was significantly greater than the 0.32 kg ha^-1 measured on the grower and sow treatments. As runoff rate increased from 3.2 to 21.2 L min^-1, runoff loads of DP, total phosphorus, NO₃-N, and total nitrogen increased from 8.4 to 40.1, 101 to 659, 420 to 2470, and 470 to 2850 g ha^-1 min ^-1, respectively. Runoff rate was an important variable significantly influencing each of the measured water quality parameters.