Sorghum Harvest Index in Relation to Plant Size, Environment, and Cultivar

Abstract

AbstractThere are reports in the literature showing that harvest index (HI) does and does not increase with increase in plant size. The slope of the upper‐bound line passing through the origin in the grain yield vs. dry matter yield plots has been proposed to approximate the “genetic” HI for a given environment and inter‐cultivar comparison. The objectives of this study were to determine what changes occur in HI of sorghum [Sorghum bicolor (L.) Moench] as plant size, environment, and cultivar vary. Several environments were established in two replicated field experiments on Pullman clay loam (fine, mixed, thermic Torrertic Paleustoll), one with eight cultivars, and the other with two cultivars, three seeding dates, and three irrigation regimes. Cultivar DK‐41Y were common to both experiments. Variation in plant size was created by thinning the original stands to varying degrees. Harvest index was determined for different plant densities based on individual plant data. Lack of non‐zero intercepts of grain‐yield vs. dry‐matter‐per‐plant regressions and constancy of HI with change in plant mass, under a given environmental condition, showed that HI was independent of plant size. Harvest index values, based both on average grain and dry matter yield, and slope of the upper‐bound line, were sensitive to environments. Upperbound HI values of cultivars DK‐42, DK‐41Y, and Sprint (0.50–0.52) were significantly higher than those of Funks 499, Richardson 9112, and DK‐46 (0.46–0.48).