Crop Utilization of Nitrogen in Swine Lagoon Sludge

Swine lagoon sludge is commonly applied to soil as a source of nitrogen (N) for crop production but the fate of applied N not recovered from the soil by the receiver crop has received little attention. The objectives of this study were to (1) assess the yield and N accumulation responses of corn (Zea mays L.) and wheat (Triticum aestivum) to different levels of N applied as swine lagoon sludge, (2) quantify recovery of residual N accumulation by the second and third crops after sludge application, and (3) evaluate the effect of different sludge N rates on nitrate (NO3-N) concentrations in the soil. Sludge N trials were conducted with wheat on two swine farms and with corn on one swine farm in the coastal plain of North Carolina. Agronomic optimum N rates for wheat grown at two locations was 360kg total sludge N ha(-1) and the optimum N rate for corn at one location was 327kg total sludge N ha(-1). Residual N recovered by subsequent wheat and corn crops following the corn crop that received lagoon sludge was 3 and 12kgNha(-1), respectively, on a whole-plant basis and 2 and 10kgNha(-1), respectively, on a grain basis at the agronomic optimum N rate for corn (327kg sludge N ha(-1)). From the 327kgha(-1) of sludge N applied to corn, 249kgNha(-1) were not recovered after harvest of three crops for grain. Accumulation in recalcitrant soil organic N pools, ammonia (NH3) volatilization during sludge application, return of N in stover/straw to the soil, and leaching of NO3 from the root zone probably account for much of the nonutilized N. At the agronomic sludge N rate for corn (327kgNha(-1)), downward movement of NO3-N through the soil was similar to that for the 168kgNha(-1) urea ammonium nitrate (UAN) treatment. Thus, potential N pollution of groundwater by land application of lagoon sludge would not exceed that caused by UAN application.