Monday, November 13, 2006 - 11:15 AM

Fertilizer Nitrogen Source and Placement, and NBPT Effects on No-Till Cotton N-Use-Efficiency.

Robert Earnest and Jac Varco. Mississippi State University, Mississippi State, MS 39762

Due to declining availability of ammonium nitrate (AN) and associated liabilities, alternate sources of fertilizer N such as urea are being explored. Although urea has commonly been used worldwide, the loss of N through NH3 volatilization has remained a limitation in its usage. Addition of a urease inhibitor could reduce losses through NH3 volatilization.  The objective of this research was to measure the effects of fertilizer N source and placement, and a urease inhibitor on N-use-efficiency of no-till cotton using the 15N isotope as a tracer in a field study.  Fertilizer N treatments were applied at total a rate of 120 lb N/acre with 50 % applied at planting and 50 % at early square.    Treatments included AN broadcast, urea broadcast, urea ammonium nitrate (UAN 32% N) subsurface banded, UAN surface dribbled, urea treated with NBPT broadcast, UAN treated with NBPT surface dribbled, and a zero rate of N.  Addition of NBPT to broadcast urea increased 15N recovery 17.6%, and performed comparably to AN in first year of study.  However, addition of NBPT to UAN treatments only increased total N uptake.  Results suggest a reduction in N loss through NH3 volatilization from broadcast urea treated with NBPT.