NITROGEN MANAGEMENT AND BUDGETS FOR IRRIGATED COTTON IN THE WESTERN USA

We present research on new and improved and updated N fertilizer management recommendations for 4-bale/acre cotton based on a 36-inch NO3-N soil test for irrigated cotton from a 2-year study on surface/furrow irrigation study and a 1-year study under sprinkler irrigation. We also compared UAN with UAN plus the N loss inhibitor Agrotain Plus. Additionally, we compared reflectancebased N fertilizer management with soil test-based management. Nitrogen balances indicated that residual soil NO3 was substantial, especially with N fertilizer rates > optimal. Recovery efficiency of N in plant ranged from 8 to 64 %. Recovery > 50 % were for the lower end of N rates (i.e. 53 to 84 lb N/ac). Net N mineralization estimated from zero-N plot N uptake ranged from 42 to 97 lb N/ac, with the high end being under sprinkler irrigation. Soil profile NO3 between 36 and 72 inches was considered leached and made up the largest N loss pathway. Deep percolation below 6 feet was estimated with a water balance and ranged from 0.1 % under a sprinkler to 23 % in surface/furrow irrigation. Agrotain Plus shows promise for mitigating N2O emissions and NO3 leaching.