Nitrogen fertilizer sources and tillage effects on cotton growth, yield, and fiber quality in a coastal plain soil

Interest in urea-ammonium sulfate (UAS) as a N fertilizer is increasing due, in part, to increased restrictions on ammonium nitrate. This has resulted in UAS being marketed as an alternative fertilizer source; however, UAS has not been widely tested. A cotton (Gossypium hirsutum L.) field study was conducted in Central Alabama from 2009 to 2011 on a Coastal Plain soil (Marvyn loamy sand; fine-loamy, kaolinitic, thermic Typic Kanhapludult) comparing UAS to two common granular fertilizers [urea, ammonia sulfate (AS)] under both conservation and conventional tillage systems. The overall objective was to determine the influence of UAS on cotton growth parameters, yield, and fiber quality. Cotton was fertilized with 101 kg N ha−1 urea, AS, or UAS 5-6 wk after planting each year. Plant growth characteristics were evaluated 3-4 wk before defoliation, and cotton yield and fiber quality were determined on the machine-harvested lint. Tillage had little influence on plant growth, while UAS and/or AS tended to produce the largest number of bolls and largest aboveground, root, and total biomass in 2009 and 2011. Lint yield was also influenced by fertilizer source in 2009 and 2011, with UAS and AS producing significantly higher yields than urea. Both tillage and fertilizer source had minimal influence on cotton fiber quality. Results suggest that UAS produces similar or greater yields than urea and is comparable to AS. However, more research is needed to determine the long-term influence of UAS on soil acidity and N loss compared to urea and AS.