Evaluation of the Nitrogen-Fertilizer Value of Poultry Litter for Winter Wheat in Arkansas.

Poultry litter (PL) has proven to be an excellent nutrient source for summer-grown crops, but information regarding its fertilizer value for winter-grown crops is lacking. Our research objective was to determine the urea-N equivalence or plant-available N of PL applied to soft red winter wheat (Triticum aestivum). Experiments were performed on silt loam soils following either rice (Oryza sativa) or soybean [Glycine max (L.) Merr.]. Poultry litter was applied at five total N rates of 67 to 336 kg N ha^-1 in October (2006 & 2007) and December (2006) and compared with wheat fertilized with 0 to 179 kg urea-N ha^-1 applied in February and March. A second experiment (2008) compared wheat response to 168 kg PL-N ha^-1 applied in October, December, February, and March with 0 to 168 kg urea-N/ha applied in February and March.  Nitrogen uptake and grain yield were measured for rate experiments, but only grain yield was measured in the application time trial.  Grain yield of wheat increased linearly as PL- and urea-N rates increased during both years, but the rate of yield increase differed between N sources.  The linear slope coefficient for urea-N ranged from 0.35 to 0.38 kg net grain yield kg^-1 N, depending on year, and was always 4.5 to 5.5 times greater than the slope coefficient for wheat receiving PL (0.064 to 0.085). In 2008, there was no difference in the yields of wheat fertilized with 168 kg PL-N ha^-1 from October through March, which produced yields that were between those of wheat fertilized with 34 to 67 kg urea-N ha^-1.  Results indicate that 5 kg PL-N applied in October or December is approximately equivalent to 1 kg urea-N applied in February-March.  Determining the specific reasons for the poor recovery of PL-N by winter wheat were beyond the scope of this study, but slow mineralization of the organic N in PL during the fall and winter months is likely.