Elevation map-based variable rate poultry litter application is a promising method in cotton production

Variable rate poultry litter (PL) application can potentially increase cotton yield and reduce environmental degradation risks associated with excess applications. The objective of this study was to determine whether applying PL in an inherently variable cotton field as variable-rate based on soil organic matter (SOM, VRo) or elevation (VRe) maps leads to greater yield and production efficiency than applying by the traditional uniform rate (UR). Poultry litter was applied by varying the rate within ±20 % of the target rates (7.9–11.2 Mg ha⁻¹) where the highest elevation or lowest SOM regions received the highest rate, and the lowest elevation or highest SOM regions received the lowest rate. A treatment fertilized with conventional synthetic fertilizers served as the standard control (Std). Cotton fertilized with PL, regardless of the application method, provided greater K, S, and P nutrition and increased lint yield by as much as 30 % relative to the Std treatment. Applying the PL by the VRe method increased the production efficiency (yield per unit applied PL) by nearly 13 % over the UR. The VRo treatment resulted in a yield reduction of up to 11.8 % but the production efficiency was 14.2 % greater than the UR treatment. Variable rate application based on SOM was not as effective as that based on elevation. The results overall show that PL was superior to synthetic fertilizers in this soil and this superiority could further be enhanced by applying the PL as variable rate based on elevation maps.