Forage Yields, Nutrient Uptake, Soil Chemical Changes, and Nitrogen Volatilization from Bermudagrass Treated with Dairy Manure

Abstract

Application of manure on cropland in association with large confined animal feeding operations, such as large drylot dairies, has raised concern about nutrient contamination of surface and groundwaters. Our objective was to determine the yield and nutrient uptake of 'Coastal' bermudagrass (Cynodon dactylon L. Pers.) and a bermudagrass sod interseeded with winter wheat (Triticum aestivum emend Thell cv. Wintex) treated with dairy waste, the fate of manure N and P in the soil, and nitrate N in soil solution. Four rates of dairy manure (target rates of 0, 100, 200, and 400 lb N/acre) were surface applied to each system from 1992 to 1995. We measured N and P harvested in forage, changes in extractable N and P concentrations in the soil, nitrate N levels in soil water, and N volatilization from surface-applied manure. Yield increased linearly with increasing manure rate each year. Only 25% of manure N and 20% or less of P were recovered in forage during the 4 yr. Analysis of soil water samples collected at 18 or 36 in. below the soil surface on 54 dates indicated < 3 ppm of nitrate N in plots treated with up to 60 tons/acre of solid dairy manure during 4 yr. The primary adverse effect of manure application to forage crops was a sixfold increase in extractable P in the surface 6 in. of soil at the highest manure rate. Nitrogen losses to the atmosphere from surface-applied dairy waste increased from 20 to a maximum of 35% as moisture content of the manure increased to 40%. Most of the N loss occurred within 6 h of waste application. These data indicate that solid dairy manure from confinement lots should be applied at rates less than 20 tons/acre per year to reduce risks of soil P buildup and nitrate N leaching.