Runoff Nutrient Loads as Affected by Residue Cover, Manure Application Rate, and Flow Rate

Manure is applied to cropland areas with varying surface cover to meet single‐year or multiple‐year crop nutrient requirements. The objectives of this field study were to: (1) examine runoff water quality characteristics following land application of manure to sites with and without wheat residue, (2) compare the water quality impacts of land application of manure to meet 0‐, 1‐, 2‐, 4‐, and 8‐year P‐based requirements for corn, and (3) evaluate the effects of varying runoff rates on runoff nutrient loads. Three 30‐min simulated rainfall events, separated by 24 h intervals, were applied at an intensity of 70 mm h‐1 to 0.75 m wide by 2.0 m long plots on which manure has been previously applied and incorporated. Runoff loads of dissolved phosphorus (DP), total phosphorus (TP), NO3‐N, NH4‐N, and total nitrogen (TN) were significantly greater on the plots with residue cover. Manure application rate significantly influenced runoff loads of DP, TP, NO3‐N, NH4‐N, and TN. No significant differences in runoff loads of DP and TP were found between sites where manure was applied to meet a 1‐year or 2‐year P requirement for corn. However, runoff loads of DP and TP were significantly greater on the sites where manure was applied to meet a 4‐year rather than a 2‐year P requirement. Each of the measured water quality parameters except electrical conductivity (EC) was significantly influenced by runoff rate. The application of manure to meet multiple‐year crop nutrient requirements may increase nutrient loads in runoff.