Evaluation of Nitrogen Fertility on Winter Wheat Forage Yield.

Winter wheat (Triticum aestivum L.) is commonly established as a source of winter and spring forage for cattle grazing in many regions of Texas and the South Plains. As of January 1, 2011, there were 1.6 million head of stocker cattle grazing small grains pastures in Texas, Kansas, and Oklahoma according to the National Agricultural Statistics Service 2010-2011 cattle inventory report. In these stocker cattle systems, managing soil fertility is an integral factor in reaching specific biomass yield goals that producers depend upon to sustain their herds. Current recommendations in Texas only specify heavy, moderate, and light levels of grazing. Thus, in the fall of 2010, a fertility study was initiated on the Brazos River flood basin located south west of College Station, Texas. The overall goal of this research was to update the nitrogen (N) rate recommendations for grazed winter wheat. The objectives of this study were; (1) to determine winter wheat forage yield potential at varying levels of N fertility and (2) to evaluate five methods of quantifying forage yield. This trial consisted of five pre-plant N rates (0, 45, 67, 90, 112 kg/ha) paired with five top-dress N rates (0, 22, 45, 67, 90 kg/ha) yielding a total of twenty-five treatments. Pre-plant N was applied as liquid urea ammonium nitrate (UAN) and drill incorporated. Top-dress applications of liquid UAN were made following each forage harvest. Five biomass evaluation methods were used including both non-destructive (visual rating, digital image analysis, and greenseeker generated normalized difference vegetative index) and destructive methods (clipping three 30.5 cm sections of linear row and full plot harvest.) Current results demonstrate the highly variable nature of forage production. Over the season, the 45 kg/ha pre-plant N with the 67 kg/ha top-dress N treatment and the 0 kg/ha pre-plant by 90 kg/ha top-dress treatment yielded better than the untreated check. In comparison to full plot harvest, the yields obtained from clippings were slightly less variable but much higher. Little to no relationship between biomass and NDVI was seen. Results will be discussed in greater depth upon further analysis.