Soft winter wheat outyields hard winter wheat in a subhumid environment: Weather drivers, yield plasticity, and rates of yield gain

Despite the proximity in zones of adaptation for soft and hard winter wheat (SWW and HWW; Triticum aestivum L.), agronomic evaluations have been confined to market class. Our objectives were to compare SWW and HWW regarding yield and agronomic attributes; genotype, environment, and their interaction; and rates of yield gain. Yield, grain volume weight, heading date, and plant height were collected from 40 adjacent studies evaluating HWW and SWW cultivars in 20 Kansas environments (n = 2,885). Growing season weather partially explained the variability in yield (47-51%), heading date (58-92%), and plant height (67-80%). Yield was greater in SWW than in HWW (3.73 vs. 3.48 Mg ha(-1)), and a quadratic relationship between the 10th, mean, and 90th percentile yields suggested that SWW has a greater yield potential than HWW, although grain volume weight was greater in HWW (743 vs. 733 kg m(-3)). An asymmetric yield response for both classes was associated with greater phenotypic plasticity, which portrayed a more positive response for SWW. We performed a literature review that suggested a greater genetic gain for SWW than for HWW (33 vs. 17 kg ha(-1) yr(-1)). This gain, however, represented a smaller portion of the regional yield gain (considering both genetic gain and adoption of agronomic practices) of each class (72 vs. 81%). We concluded that SWW outyields HWW due to greater rates of genetic gain, partially due to breeding in higher yield environments, and more positive phenotypic plasticity of yield in high-yielding environments coupled to yield stability in excessively moist environments.