Evaluation of best management practices to reduce nutrient contaminant losses in runoff from broiler litter-amended soils. II. Grass cover.

摘要

The effect of Bermuda grass [Cynodon dactylon (L.)] cover on sediment and nutrient runoff losses from untreated as well as from broiler litter (with alum)-amended soil was evaluated. Runoff generated from a completely bare soil had significantly higher runoff volumes, as well as more suspended solids (SS), total phosphorous (TP), and total Kjeldahl nitrogen (TKN) concentrations than soils with >=80% grass coverage. In addition, bare soils exhibited less time to runoff (time span between rainfall initiation and the start of runoff) than the grass-covered treatments. Average TP and TKN concentrations in runoff from experimental trays having 2 80% grass coverage were reduced by 93% and 89.5%, respectively, as compared to concentrations in bare soil runoff. Similarly, suspended solid concentration showed a reduction of 99% over that of the bare soils. Dissolved P (DP) concentration losses were well below the 1 mg/L limit suggested to control P contamination from agricultural lands, even for the broiler litter-amended soils. In general, both TP and TKN concentrations followed the trend established by suspended sediment losses. In contrast, nitrate exhibited a negative correlation with SS concentrations. Applications of broiler litter caused significant increases in the dissolved constituents (i.e., DP and NO₃-N) concentrations in runoff but not in those constituents (i.e., TP and TKN) for which sediment losses represent a significant transport mechanism. A significant decrease in SS concentrations was observed with time at both cover categories, with losses being much higher from the bare soils than from the grass-covered soils. Broiler litter applications caused a significant reduction in SS concentration losses at each grass cover category (although much higher losses were observed from bare soils). The combination of alum application and a good grass cover (>=80%) reduced estimates of sediment, TP, and TKN runoff export loads by more than 95% relative to that of the runoff from bare soil.