Tuesday, November 14, 2006 - 8:00 AM

Spectral Reflectance Based Nitrogen Management for Subsurface Drip Irrigated Cotton.

Rajkumari Yabaji1, Kevin Bronson2, Cary Green3, Eduardo Segarra1, and Adinarayana R. Malapti4. (1) Texas Tech Univ, 1612 Ave Y, Apt # 201, Lubbock, TX 79401, (2) Texas A&M University - Rangeland Ecology & Management, Texas A&M Univ.Agric. Exp.Sta, Route 3 Box 219, Lubbock, TX 79403, (3) Texas Tech Univ, Plant & Soil Science Dept, 15th and Detroit, Lubbock, TX 79409-2122, (4) Texas A & M Ag Experiment Station, 1102 E FM 1294, Lubbock, TX 79403

 Subsurface drip irrigation (SDI) systems for cotton production greatly minimizes water constraints, and nitrogen management becomes the main priority.  Injecting N fertilizer into SDI systems should in theory be as efficient as the irrigation delivery system itself is.  However, previous research by the Texas A&M University – Texas Agric. Exp., Stn. Soil Fertility Program at Lubbock, TX has indicated that plant uptake of  N fertilizer in SDI cotton is < 50 % of injected N.  This research aims to improve N fertilizer management in SDI cotton.  We tested two fluid N fertilizer sources: urea ammonium nitrate (UAN) vis a vis UAN plus ammonium thiosulfate (ATS).  The ATS source theoretically acts as an N stabilizer against nitrification and denitrification losses.  We also aimed to fine-tune the timing of N fertigation by comparing UAN injection from 20 June to 22 July with UAN injection from 20 June to 12 August.  Finally, we tested spectral reflectance-based timing of N fertigation from 20 June to 12 August.  Our results showed that lint yields with UAN plus ATS did not differ from UAN alone.  Timing of N fertilizer injection also did not affect lint yields.  Lint yield with the reflectance-based treatment was not significantly different from yields with the other N-fertilized treatments. The most encouraging result of this study was the savings of 25 lb N/ac that was realized with the reflectance-based treatment (N rate was 65 lb N/ac) relative to the other N-fertilized treatments, which received 90 lb N/ac. Recovery efficiency of injected N averaged 63%.  Second year results will be presented.