GRAIN-SORGHUM YIELD RESPONSE TO NONUNIFORM STAND REDUCTIONS

Nonuniform stand reductions caused by poor emergence, insect damage, o r other factors, occur frequently in grain sorghum [Sorghum bicolor (L .) Moench] fields. This research was conducted to determine the effect of within-row skip patterns on grain yield and yield component compen sation, particularly for hybrids differing in tillering ability. Dryla nd field studies were conducted at Manhattan (Reading silt loam, fine- silty, mixed, mesic Typic Argiudoll) and St. John (Naron fine sandy lo am, fine-loamy, mixed, thermic Udic Argiustoll), KS, during 1988 and 1 989. Two medium-maturity hybrids, DeKalb DK-46 and Pioneer 8500 were s elected based on low and high tillering ability. Plots were three rows , with the middle row containing a within-row skip pattern. Results we re analyzed separately by skip row, adjacent row, and average for the three rows. Skip lengths within a 7.6-m row were 0.9 m, 0.9 m repeated three times, and 2.7 m within the skip row, and the 0.9 m x 3 pattern in all three rows. Yield of the skip row was reduced by every configu ration bordered by control stand adjacent rows. Yield compensation fro m adjacent rows and within the skip row compensated for reduced stands , except for a 2.7-m skip resulting in 5,1% yield reduction, 64% unifo rmly spaced stand in all three rows with 6.9% yield reduction, and thr ee 0.9 m within-cow skips in all three rows with 10.9% yield reduction . Compensation was primarily in number of heads per plant and seeds pe r head, Difference in hybrid tillering response did not influence grai n yield. Thus, yield reduction is likely only where skips result in se vere plant spacing nonuniformity.