Improving Nitrogen Management for Subsurface Drip-Irrigated-Cotton in Arizona

Surface irrigation is the predominant irrigation mode in the far Western US for cotton.  Subsurface drip irrigation, on the other hand has minimal evaporative and deep percolation losses, and also provides high nitrogen (N) use efficiency.  We tested a 3-foot soil nitrate test algorithym for a 4 bale/acre yield goal at 100 % and 75 % ET replacement.  At the full irrigation, we also tested a canopy reflectance-based N management approach.  Urea ammonium nitrate fertilizer was fertigated for a 6-week period starting at first square.  Total N injected was 156 and 141 lb N/ac for soil test and reflectance treatments at 100 % ET, respectively.  Lint yields were at 1400 lb lint/ac for those two treatments.  Soil test N management at 75 % ET resulted in 1100 lb lint/ac.  Recovery efficiency of fertigated N ranged from 59 to 81 %.