Determination of Poultry Litter's Nitrogen-Fertilizer Value for Winter Wheat Production.

The availability of N in poultry litter (PL) applied in the fall as a nutrient source for winter wheat (Triticum aestivum L.) production has not been adequately characterized.  Our research objective was to determine the grain-yield based, inorganic-N fertilizer equivalence of PL applied preplant or at-planting to winter wheat.  Six field experiments were established in 2009 and 2010 on silt loam soils in Arkansas.  Plots received 0, 84 and 168 kg N ha^-1 as PL applied preplant and/or at-planting.  The inorganic-N fertilizer equivalency of PL-N was based on grain yield response of wheat fertilized with 22 to 191 kg N ha^-1 applied in late winter as a urea and ammonium sulfate blend (UASB).  Wheat yield responses to UASB-N were characterized using either a linear or quadratic model.  Yields of wheat receiving no N ranged from 1722 to 3714 kg ha^-1 and maximal yields of 3734 to 5854 kg ha^-1 were produced with UASB-N.  Wheat yields responded to UASB-N rate in a quadratic manner at four site-years and linearly at two site-years.  Wheat receiving 84 kg PL-N ha^-1, averaged across PL application times, produced yields that were 583 to 1049 kg ha^-1 greater (p<0.10) than the no N control at five of six site-years.  Application of 168 kg PL-N ha^-1 increased yields by 490 to 1224 kg ha^-1 above that of 84 kg PL-N ha^-1 at only three site-years.  Application time resulted in different wheat yields at only one site-year (at-planting > preplant).  Application of 84 to 168 kg PL-N ha^-1 produced yields equivalent to 0 to 132 kg UASB-N.  Thus, the UASB-N equivalence of total PL-N ranged from 0 to 70% with an overall average of 35%.  Based on these results, on average, only 35% of the total PL-N should be credited towards the recommended N rate.