Spring Wheat Response to Nitrogen Fertilizer Rate and Application: A Conventional and No Tillage Comparison.

No tillage (NT) systems, versus conventional tillage (CT) systems, can influence nitrogen availability due to lower soil temperature; plant growth differences; and higher residue, organic matter, biological activity, and water availability. Nitrogen fertility is critical for hard red spring wheat (HRSW) grain production, protein level, quality, and value. This study near Genesee, Idaho, USA evaluated nitrogen fertilizer rates of: 56, 84, 112, 140, 168, and 197 kg ha^-1 and application timings of: 100% at planting, 70% planting + 30% anthesis, and at planting + 22 kg ha^-1 foliar at anthesis in a NT and CT tillage comparison. The HRSW ‘Scarlet’ followed winter wheat in a three year rotation with dry pea before winter wheat. Between NT and CT, average HRSW grain yields and responses to N fertilization varied year to year, but were not different over years 2006-2010 and averaged 3,325 kg ha^-1. Averaged over years, optimum nitrogen fertilizer rates were found at 140 kg ha^-1 producing 3505 kg ha^-1 of grain in CT and at 196 kg ha^-1 producing 3670 kg ha^-1 of grain in NT. Grain protein across years and N rates was 0.9% lower in NT than CT. Regression of protein and N rate shows protein increased at 0.122% per 10 kg ha^-1 N in CT and 0.110% per 10 kg ha^-1 N in NT. Protein regression lines were not different in slope but were different in level between tillage treatments. Both grain density and seed weights were higher in NT than CT, decreased with N rate, and regressions were different in level but not slope. Split N applications only produced slightly higher grain density, seed weight and harvest index, but did not significantly influence other characteristics. Equivalent yields, higher test weights and seed weights, but lower protein are benefits and drawbacks of NT compared to CT.