17 Jun Uneven Stands in Grain Sorghum
Uneven Stands in Grain Sorghum
Sorghum responds to its environment more than many of our management decisions. Seeding rates are important because they affect the final stand we achieve in a field. Sorghum yield components (head per plant, seed per head, and seed size) are extremely elastic and allows the crop to respond to the environment.
This spring has been a challenge for sorghum planting because we have had places with too much moisture, which can cause planter performance issues, and places where we experienced drought which can result in variable stands because the soil does not dry uniformly. Unlike corn, sorghum stand uniformity and skips seldom affect sorghum yields because of the sorghum yield component elasticity.
If we have skips in our grain sorghum stand because of stand establishment, the sorghum plant can adjust to the situations easily. We typically will see higher heads per plant (tillers) because of tiller survival is determined by light interception at the base of the plant. Final seed per head is determined later and responds to growth rates or stress levels experienced closer to heading and is affected by the number of heads the plant produced.
Research conducted at Kansas State University back in the late 1980s examined how skips in sorghum stands affect yields (E. Larson and R. Vanderlip. Agron J. 86:476). All stands in this study were hand thinned early after planting so that the plants had adequate time to produce productive tillers. The treatments are illustrated in figure 1 and included: 100% stand, 64% stand uniform across all five rows, one – 3 foot skip in the middle row with the adjacent rows at 100% stand, three – 3 foot skips in the middle row with the adjacent rows at 100% stand, one – 9 foot skip in the middle row with the adjacent rows at 100% stand, and finally three – 3 foot skips in the middle three rows with the adjacent rows at 100% stand.
Figure 1. Grain sorghum skip patterns (adapted from E. Larson and R. Vanderlip. Agron J. 86:476)
Because of grain sorghum’s ability to compensate or adjust to the environment around it, yields were not affected significantly when the stand was uniformly reduced (64% stand) or the skips in an individual row were small and the rows around the skips had good stands. Large skips across the entire plot were the only plots that reduced yields. The 9-foot skip reduced grain yields by 5.1% and the three 3-foot skips across the plot rows reduced grain yields by 9.9%.
These results illustrate that sorghum can compensate for missing plants or uneven stands in grain sorghum unless the stands have very large skips or multiple skips in adjacent rows. The yield losses are not large and, in most cases, trying to replant the field would result in larger yield losses because of the later planting date. Large skips in fields could cause challenges with weed control since the field will not have a complete canopy and be less competitive with weeds in those areas and should be scouted frequently to make sure that weed pressure does not become too high in these areas.