Equivalency of broiler litter to ammonium nitrate as a cotton fertilizer in an upland soil
Estimates of litter value based on crop yield equivalency to inorganic fertilization may reflect the actual value of litter more accurately than estimates based on its N, P, and K content. The primary objective of this research was to identify a rate of broiler litter that results in cotton lint yield equivalent to inorganic N fertilization and to estimate litter value based on this yield equivalency. The research was conducted in northern Mississippi in 2002 to 2004 in a Loring silt loam upland soil. Cotton was fertilized with six broiler litter rates ranging between 2.2 and 13.4 Mg ha–1 or six NH4NO3–N rates ranging between 34 and 168 kg ha–1 or was not fertilized. Lint yield calculated based on fitted models peaked at 1033 kg ha–1 when cotton was fertilized with 94 kg ha–1 NH4NO3–N, which is similar to the 90 kg N ha–1 local recommendation. Lint yield of cotton fertilized with litter (8.7 Mg ha–1) peaked at 1156 kg ha–1, which is a 123 kg ha–1 lint yield increase over NH4NO3–N. The economic optimum NH4NO3–N rate was 72 kg ha–1, which produced 88 kg ha–1 less lint than the economic optimum litter rate of 5.2 Mg ha–1. Fertilization with 3.7 Mg ha–1 litter produced lint yield equivalent to the locally recommended 90 kg ha–1 NH4NO3–N. The N fertilizer replacement value of litter calculated based on this equivalency exceeded the value calculated using the traditional method by 27%. These results overall show that fertilizing cotton in this soil with litter increased lint yield above that possible with conventional inorganic fertilization by 12% and that broiler litter is substantially more valuable than can be estimated from its N, P, and K contents.