Tillage and N requirements for wheat planted into corn residue

Context Corn (Zea mays, L. ) generates significant surface residue, which can require intensive surface tillage and increased N fertilizer rates to optimize subsequent wheat (Triticum aestivum, L. ) production. However, surface tillage degrades soil health benefits, while unnecessary N applications reduce profits. Therefore, identifying the correct surface tillage level and N rate combination is critical to optimize wheat yields and profits following corn production. Methods A split plot treatment restriction in a randomized complete block design with three blocks was used to evaluate surface tillage levels and N fertilizer combinations for wheat following corn over four non-consecutive growing seasons (2016–17, 2017–18, 2019–20, 2020–21) on a Decatur silt loam (fine, kaolinitic, thermic Rhodic Paleudult) in northern Alabama, USA. Tillage systems conventional tillage (CT), mulch tillage (MT), light disk (LD), and no tillage (NT) were main plots and fall and spring N rate (67, 101, and 134 kg N ha −1) combinations applied as urea-ammonium nitrate 28% solution were subplots to evaluate early season wheat growth (tiller density, tiller biomass, and tiller N uptake), in-season wheat growth (biomass and N uptake), wheat yields, nitrogen use efficiency (NUE), and net returns. Results Fall N increased early season wheat growth parameters up to 25%. In-season N uptake varied across tillage systems with inconsistent responses to split applications across N rates. The CT, MT, and LD systems yielded 23% greater than the NT system across N treatments and growing seasons. Grain NUE averaged 38. 7% across growing seasons for all tillage and N treatments. Average net returns were US733 ha −1 (MT), US643 ha −1 (LD), US601 ha −1 (CT), and US468 ha −1 (NT). Conclusions Wheat growth and production declined when planted into corn residue as surface tillage decreased. This effect was further exacerbated with low N applications. Fall N applications enhanced early season wheat growth, but a split application of the remaining N did not increase wheat yields compared to the corresponding single rate application. Therefore, split N applications did not benefit wheat production following corn compared to single N applications across N rates and conditions examined in this experiment. Applying 134 kg N ha −1 maximized wheat yields and net returns for NT, but results indicated greater N rates above current recommendations across all tillage systems following corn could be justified.