Grain, Dry Matter Yield Relationships for Winter Wheat and Grain Sorghum—Southern High Plains

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Abstract
Grain yield of cereal crops is closely associated to the aerial (above ground) dry matter yield, but predictions of grain yield based on model estimates of dry matter yield are often inaccurate due to variations in the assumed harvest index. This study analyzed the relationship between grain yield and aerial dry matter yield from published studies for winter wheat [Triticum aestivum (L.)] and grain sorghum [Sorghum bicolor (L.) Moench) conducted at Bushland, TX in the Southern High Plains. Harvest index (HI) was defined and determined as the slope of the linear relationship between Yd, plant grain yield in Mg ha−1 on a dry basis, and DM, aerial (field) dry matter yield in Mg ha−1, as contrasted to the traditional definition of HI as the ratio YdDM. Simple linear relationships had coefficients of determination of 0.95 for the seven grain sorghum experiments and 0.75 for the five winter wheat experiments at Bushland and standard errors of the estimates of 0.47 Mg ha−1 and 0.63 Mg ha−1, respectively. The HI of winter wheat and grain sorghum at Bushland was 0.35 and 0.47, respectively, and largely unaffected by fertility, water use, row spacing, and many other cultural practices like tillage and profile modification, and growing season environment. The linear regressions indicated a significant (0.05 probability level) intercept value of −0.53 Mg ha−1 for grain sorghum while the intercept value 0.16 Mg ha−1 for winter wheat was not significant (0.05 probability level).