Irrigated Cotton Response to Nitrogen Sources and Rates in the Southern High Plains of Texas.

Cotton (Gossypium hirsutum L.)  is the main crop in West Texas. Management strategies to increase nitrogen (N) use efficiency from cotton production depend on selecting the right N source. However, the use of potential N sources on cotton cultivated in the Southern High Plains of Texas have not been well studied. A field study was conducted with the cotton cultivars Fiber Max GT (FM 2011) and Deltapine 1212 B2RF (DP1212) grown in an  Amarillo–Acuff sandy clay loam soil at the Quaker Avenue Research Farm in Lubbock, TX. We compared the effect of polymer-coated urea (PCU) [Environmentally Smart Nitrogen® (ESN) containing 44% N as urea], Entec® 21 containing 21% N as ammonium sulfate with the nitrification inhibitor 3,4-dimethylpyrazol phosphate (DMPP), urea containing 46% N, and Utec® containing 46% N as urea with the urease inhibitor N-(nbutyl) thiophosphoric triamide (NBPT) at rates of 45 and 90 kg N ha^-1 (50 and 100 % of recommended rate) on plant N nutrition, lint yield, and agronomic efficiency. No significant differences in cotton leaf N concentration were observed between N treatments. However, FM 2011 cultivar had higher lint yield with UTEC at 45 kg N ha^-1 rate compared to Entec at 45 kg N ha^-1, which also promoted greater lint yield than control. In the DP1212 cultivar, Entec at 45 kg N ha^-1 rate resulted in higher lint yield than almost all of treatments, except PCU at 90 kg N ha^-1 rate. Urea treatments had higher lint yields than control only. In both cultivars, agronomic efficiency was generally higher at 45 kg N ha^-1 rate. However, Entec at 45 kg N ha^-1 rate resulted in highest agronomic efficiency in the cultivar DP1212.