Plant population and fungicide economically reduce winter wheat yield gap in Kansas

Abstract

Winter wheat (Triticum aestivum L.) water limited 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 reduce wheat yield gaps (YG) economically. 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 Manhattan, Belleville, and Hutchinson Kansas. Sites were combined based on tillage practice, growing region in Kansas, and disease pressure. Thus, Manhattan had low disease pressure, was no-tilled, and in eastern Kansas for 2015-16 and 2016-17 (two site years). Meanwhile, Belleville and Hutchinson had high disease pressure, were conventionally tilled, and in central Kansas for 2015-16 and 2016-17 (four site years). We individually added six treatments to a farmer’s practice control (FP) or removed from a water-limited yield control (Y[subscript]w), which received all treatments. Practices were additional split-nitrogen (N), sulfur (S), chloride (Cl), increased plant population, foliar fungicide, and plant growth regulator (PGR). Percent YG was calculated by block and site-year using the Y[subscript]w as reference for potential yield. Orthogonal contrasts indicated yield under no-till which had low disease pressure increased from the FP by the full Y[subscript]w (+0.37 Mg ha⁻¹), but also by the individual practices split-N (+0.28 Mg ha⁻¹), S (+0.26 Mg ha⁻¹), increased plant population (+0.36 Mg ha⁻¹), and fungicide (+0.18 Mg ha⁻¹). In the conventional till which had high disease pressure, wheat yield was increased by 1.18 Mg ha⁻¹ from the Y[subscript]w and by 1.44 Mg ha⁻¹ from the fungicide. The Y[subscript]w and split-N increased grain protein concentration in no-till and conventional-till on average by 9 g kg-1 and 12 g kg-1, respectively. Across all inputs, orthogonal contrasts indicated that the FP yield gap was 8% in no-till which had low disease pressure. Likewise, the orthogonal contrasts indicated that across individual treatments the YG was reduced by split-N (6%), S (5%), Cl (3%), increased plant population (8%), and fungicide (4%). Meanwhile, orthogonal contrasts indicated that the FP yield gap was 20% across all inputs and across individual inputs reduced to 5% from fungicide under conventional-till which had high disease pressure. Fungicide increased net return (+$106.57 ha⁻¹) under conventional-till which had high disease pressure, and increased plant population under no-till which had low disease pressure (+$36.65 ha⁻¹). While a high-cost input (i.e. fungicide) only economically reduced YG greater than 20%; however, a low-cost input (i.e. increased plant population) economically reduced YG less than 20%.