Corn Yield, N Uptake and N Efficiency Responses To Rate and Timing Of “Shallow” Anhydrous Ammonia Applications.

There has been very little research on corn (Zea mays L.) response to different nitrogen (N) rates or N timing when anhydrous ammonia (NH₃) is applied using the new shallow NH₃ applicator (JD 2510H). This study investigated the effect of timing/placement of shallow NH₃ on corn grain yield (GY), N recovery efficiency (NRE), and N use efficiency (NUE) at multiple N rates. Field experiments using RTK precision-guided equipment were conducted near West Lafayette, IN, between 2010 and 2012. Three application timings (100% pre-plant in spring just days before planting, 100% side-dress at V6-7 growth stage, and split NH₃ applications) and four N rates [0, 90, 145, and 202 kg N ha^-1 (0, 80, 130, and 180 lbs N A^-1 respectively)] were evaluated in a factorial combination. All pre-plant NH₃ was injected to a depth of 12 cm (4.5”) parallel to, but about 15 cm (6”) offset from, the intended corn rows. Side-dress NH₃ was applied in the traditional mid-row position. Corn GY treatment means ranged between 7 and 13.7 Mg ha^-1 (110 and 218 bu A^-1) in 2010-11 and between 8.6 and 11.6 Mg ha^-1 (137 and 185 bu A^-1) in 2012. Corn GY, total biomass production, and whole-plant N accumulation at maturity increased significantly with N rates in 2010-11, but corn response to NH₃ in 2012 was limited by severe drought stress. Highest GY was observed in the side-dress 202 kg N ha^-1 rate in 2010-11, but with the pre-plant 202 kg N ha^‑1 rate in 2012. However, whole-plant N uptake was the highest in the pre-plant 202 kg N ha^‑1 treatment in both 2010-11 and 2012. Pre-plant NH₃ application improved NRE slightly in 2010-11 but significantly in 2012, relative to side-dress NH₃ (whole-plant N recovery equaled ~67% of applied N fertilizer across pre-plant N rates in 2010-11 and 2012). Average NRE and NUE (yield gain to the added fertilizer compared to 0 N treatment) declined with increasing N rates as expected. Although overall NUE levels in 2012 declined by >55% in 2010-11 to drought, pre-plant and split NH₃ applications achieved much higher NUE than side-dress applications [14.7, 13.4 and 4.8 kg grain kg^-1 applied N, respectively (0.26, 0.24, and 0.09 bu. grain lb^-1 N)]. This 3-year study highlighted the GY and NUE vulnerability of one-time NH₃ application strategies in corn production with inclement weather, and the occurrence of sometimes wide divergences between NRE and NUE in treatment responses to both NH₃ rates and timing.