No-till (NT) production systems, especially winter wheat (Triticum aestivum L.)-summer crop-fallow, have increased in the central Great Plains, but few N fertility studies have been conducted with these systems. Therefore, winter wheat (W) response to N fertilization in two NT dryland crop rotations, wheat-corn (Zea mays L.)-fallow (WCF) and wheat-sorghum (Sorghum bicolor L.)-fallow (WSF), on a Platner loam (fine, smectitic, mesic Aridic Palleustoll) was evaluated for 9 yr. Five N rates, 0, 28, 56, 84, and 112 kg N ha(-1), were applied to each rotation crop. Wheat biomass and grain yield response to N fertilization varied with year but not with crop rotation, increasing with N application each year, with maximum yields being obtained with 84 kg N ha(-1) over all years. Based on grain N removal, N fertilizer use efficiency (NFUE) varied with N rate and year, averaging 86, 69, 56, and 46% for the 28, 56, 84, and 112 kg ha(-1) N rates, respectively. Grain protein increased with increasing N rate. Precipitation use efficiency (PUE) increased with N addition, leveling off above 56 kg N ha(-1). A soil plus fertilizer N level of 124 to 156 kg N ha(-1) was sufficient to optimize winter wheat yields in most years in both rotations. Application of more than 84 kg N ha(-1) on this Platner loam soil, with a gravel layer below 120 cm soil depth, would more than likely increase the amount of NO3-N available for leaching and ground water contamination. Wheat growers in the central Great Plains need to apply N to optimize dryland wheat yields and improve grain quality, but need to avoid over-fertilization with N to minimize NO3-N leaching potential.
