Which Management Strategies Are Required to Economically Reduce Winter Wheat Yield Gaps?.

Winter wheat (Triticum aestivum L.) yield potential in Kansas averages ~5.2 Mg ha^-1; however, state-level yields rarely surpassed 3.4 Mg ha^-1. Our objective was to quantify the contribution of individual management practices to economically reduce wheat yield gaps (YG). An incomplete factorial treatment structure established in a randomized complete block design with six replications was used to evaluate 14 treatments during two years in three central Kansas locations. Sites were combined based on tillage practice (no-till, Manhattan, 2016 and 2017; conventional-till, Belleville and Hutchinson, 2016 and 2017). We individually added six treatments to a farmer practice (FP) or removed from an water-limited yield (Y_w), which received all treatments. Practices were additional split-nitrogen (N), sulfur, chloride, increased plant population, foliar fungicide, and plant growth regulator. Percent YG was calculated by site-year using the Y_w as reference for potential yield. Orthogonal contrasts indicated yield under no-till increased from the FP by the full Y_w (+0.37 Mg ha^-1), but also by the individual practices split-N (+0.28 Mg ha^-1), sulfur (+0.26 Mg ha^-1), increased plant population (+0.36 Mg ha^-1), and fungicide (+0.18 Mg ha^-1). Yield under conventional-till increased by Y_w (+1.18 Mg ha^-1) largely led by fungicide (+1.44 Mg ha^-1). The Y_w and split-N increased grain protein concentration in no-till (8.6 and 9.0 g kg^-1) and conventional-till (12.3 and 11.5 g kg^-1). FP yield gap was 8% in no-till, and was reduced by split-N (6%), sulfur (5%), chloride (3%), increased plant population (8%), and fungicide (4%). FP yield gap was 20% under conventional-till and was reduced by fungicide (25%). Fungicide increased net return (+$106.57 ha^-1) under conventional-till, and increased plant population under no-till (+$36.65 ha^-1). While a high-cost input (i.e. fungicide) can only economically reduce YG when this is greater than 20%; a low-cost input (i.e. increased plant population) can economically reduce smaller YG.