Cotton Yield Benefits from Poultry Litter Applied As Variable Rate

Fields are inherently variable in soil organic matter, texture, nutrient levels, and other soil properties. So applying manures and fertilizers at uniform rates across fields results in applications below or above the needed rate. Site-specific technology, which has the potential to reduce or eliminate the over- or under-application, has not be studied for applying poultry litter in cotton production. The objective of this research was to develop and test methods of variable-rate poultry litter application based on soil organic matter (SOM) or elevation in fields with known spatial variability. The benefit of poultry litter applied by three methods (variable rate based on SOM maps, variable rate based on elevation maps, and a uniform rate that placed the same amount of manure regardless of the soil variation in SOM or elevation) to cotton yield was tested on a 10-acre no-till cotton farm in MS between 2014-2018. For comparison, a treatment that received fertilization with synthetic fertilizers to mimic the respective farmers’ practice was included. The results showed that, regardless of the method of application, poultry litter increased lint yield by a 5-yr average of 14% over the farm standard fertilization. The results further showed that applying the litter by varying the rate based on elevation where higher rates are applied at higher elevations and lower rates at lower elevations may further enhance the superiority of the litter. SOM-based maps may work also but the difficulty of generating accurate SOM maps may preclude it from being a reliable method.