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• Some of the additional grain sorghum acreage is targeted for a double-crop with wheat, but that may not be such a good idea says North Carolina State University Grain Specialist Randy Weisz.
GRAIN SORGHUM acreage increased from 10,000 to 50,000 acres in North Carolina this year.
The bottom line in the Southeast is that there is no definitive answer as to how much wheat yield may be lost, if any, when planting in a double-crop with grain sorghum.
“We simply don’t know how big a problem wheat double-cropped with sorghum may be, but growers who want to plant wheat following sorghum should know that this might be a problem for them,” Weisz says.
Production recommendations almost always come after several years of intensive university research, but there has not been much interest in grain sorghum in recent years in the Upper Southeast, therefore little research of any kind has been done on the crop.
“Because very little research has been done in this area, it is difficult to make recommendations to assist folks who want to do this. But, here are several suggestions that may help,” Weisz says.
• Use glyphosate to kill the sorghum prior to harvest. If the sorghum is left alive and starts to regrow after harvest, the new roots will continue to exude the toxic compound.
• Use tillage to incorporate sorghum residues and hasten their decomposition.
• Delay wheat planting. This is tricky. Delaying wheat planting can in-and-of-itself reduce wheat yield, but it may also help to allow the toxic compounds to decompose.
• Make sure the wheat is treated to high pre-plant fertility levels. Make sure pre-plant N, P, K, and S are at or above recommended levels.
• If planting wheat after tillage, check stand establishment and watch early tillering. The problems are most likely to show up early in the season and look like either a poor stand, or a good stand that starts to go backwards. Early nitrogen in February may help.
• If planting wheat no-till, watch the wheat plants both early for stand establishment, tillering (and need for February nitrogen), and also in the spring. Research has shown the problem may not start in no-till wheat until the spring when plants may begin to turn yellow and abort tillers.
Allelopathy also might be reduced by proper management of the sorghum residue. After the toxic compounds leach from the residue, they are degraded into harmless chemicals by microorganisms in the soil.
Tillage of the residue undoubtedly affects leaching and degradation of the allelopathic compounds, but the most effective methods have not been determined.
Research in the Midwest indicates that growers may get some idea of what level of yield loss they can expect based on when and how grain sorghum was planted.