Yield Responses of 16 Winter Wheat Cultivars to Row Spacing and Seeding Rate¹

Grain yields of winter wheat ( Triticum aestivum L.) may increase as the spacing between rows is decreased. Results in previous studies have varied with other management variables and environments, however, and only one or a few wheat genotypes were used in any one study. We used a wide genetic base of 16 cultivars to obtain estimates of yield response at two row spacings and two seeding rates to determine if there was a consistent response across cultivars and years. Row spacings of 64 and 192 mm were compared at seeding rates of 377 and 538 kernels m −2 . There were large year ✕ row spacing and year ✕ seeding rate interactions. The narrow row spacing treatments averaged 6.8 and 5.3% more grain than the standard spacing in 1983 and 1984, respectively. Cultivar responses to narrow row spacing ranged from 1.1 to 17.4% in 1983, and from −8.0 to 19.7% in 1984. No response to seeding rate was observed in 1983, but the higher seeding rate yielded 7.1% more grain in 1984 when tillering was low. A significant row spacing ✕ seeding rate interaction was detected over both years as 9.1% increase in grain yield was observed with both narrow row spacing and high seeding rate compared to wide row spacing and low seeding rate. We concluded that (i) row spacings narrower than the conventional 192‐mm spacing have the potential to significantly increase grain yields, but the response may vary depending on the cultivar and environmental conditions, and (ii) a combination of increased seeding rate and narrow row spacing is important for increasing grain yield.