Optimization of row spacing and nitrogen fertilization for cotton

Ultra-narrow row (UNR) cotton (Gossypium hirsutum L.) is a production system using high plant populations in reduced row spacings. The responses of this production system to nitrogen fertilizer have not been fully investigated. Evaluations of yield and earliness of harvest are also important. A three-year study was conducted at the Texas Agricultural Experiment Station farm, Burleson County, TX, on a Ships clay (very-fine, mixed, active, thermic Chromic Hapluderts) and a Weswood silty clay loam (fine-silty, mixed, superactive, thermic Udifluventic Haplustepts). A split plot design was used. Nitrogen fertilizer rates of 0, 50, 101, and 151 kg N ha-1 were applied as the whole plots and row spacings of 19, 38, and 76 cm were established as the split plots. Data included lint yield and yield components, as well as earliness of crop maturity and earliness-related parameters such as boll distribution. Lint yield was increased by higher nitrogen rate. There was no nitrogen rate by row spacing interaction on lint yield, implying fertilizer rates do not need to be changed for UNR systems. Reductions in row spacing did not significantly affect lint yield in any year. Responses such as reduced bolls per plant, increased plant populations, increased ginout, and decreased boll size were often significant and combined to allow the crop to maintain equivalent yields as row spacings were reduced. The slight UNR earliness advantages were probably due to changes in boll distribution. Based on these results, increases in lint yield and earliness may not reliably contribute to the profitability of UNR cotton.