Cotton Physiological Responses to Application of Urea with NBPT and DCD Under Normal and High Temperature Conditions

Nitrogen fertilization is one the most expensive agricultural practices and crops are known to recover only 30-35% of the N fertilizer applied Recently, attention has been focused on studies to measure and maximize plant N use efficiency. A practice commonly recommended to improve N fertilizer use efficiency is the addition of urease and/or nitrification inhibitors into N fertilizers.  N-(n-butyl) thiophosphoric triamide (NBPT) is a used urease inhibitor that delays hydrolysis of urea fertilizer and thereby diminishes ammonia volatilization losses. Dicyandiaminde (DCD) is a nitrification inhibitor that hinders the conversion of ammonium to nitrate lowering N loss by leaching. The objective of this growth chamber study was to evaluate the effect of use of NBPT and DCD in urea fertilization on the physiology and growth of cotton under normal and high temperatures.  Treatments consisted of two day temperature regimes, 38^oC and 30^oC, and 5 nitrogen fertilization applications: (T1) unfertilized control; (T2) 125 kg/ha of urea fertilization, (T3) 93 kg/ha of urea fertilization (T4) 93 kg/ha urea with NBPT fertilization, (T5) 93 kg/ha urea with NBPT and DCD fertilization. Nitrogen fertilization was split-applied with half incorporated pre-plant, and remaining half side-dressed at the pinhead stage. There was no two way interaction effect between temperature regime and N treatment, indicating that the N applications methods were not influenced by temperature conditions.  As expected, in comparison with N fertilized treatments, unfertilized control treatment exhibited inferior performance in all parameters collected. Overall the best N treatments were the application of 125 kg/ha of urea followed by treatment of 93 kg/ha urea with NBPT and DCD. Similar results were observed between 93 kg/ha of urea fertilization with and without NBPT fertilization. Additional research is planned to address the potential use of NBPT and DCD to increase cotton N use efficiency for improved fiber yields.