Heavy rains have thinned out some soybean stands and inclement weather has reduced the cotton acreage from what was intended. Calls are coming in about replanting poor soybean stands or replanting from cotton to corn or soybeans.
Replanting Poor Soybean Stands: At this point I would consider keeping a low but uniform soybean stand. Low meaning 80-100 thousand plants per acre that are pretty uniform– especially if beans are planted on narrow rows. Fields with extremely poor stands or complete bare areas should be replanted or spot replanted to fill in the holes in stand. Maturity group 4 and 5 varieties have the best fit now. Where only spot replanting is needed, do it early while the existing crop is small. Use the same variety or at least a similar maturity bean for a more uniform crop later in the season. Timely weed control will be important in fields with thinner stands that canopy late.
Replanting Cotton to Alternate Crop: Soybeans are the best fit for a mid June planting, however high amounts of nitrogen fertilizer will reduce and delay nodulation on a bean crop. We figure that at least half of the nitrogen applied to replant cotton fields is still available unless the field went under water for several days. In some work in Jackson in 2010, we showed reduced soybean nodulation with 50 lbs N at planting and in a dry year we had some yield loss with those treatments (probably because microbial activity is already hindered in droughty soils). Data from other states suggest that although nodulation is delayed by soil N, we may not see yield reductions with N rates up to 100 lbs where soil moisture is decent during the growing season. This year’s result may be somewhere in the middle. Corn will certainly help us utilize the nitrogen already applied for the cotton, but expect lower yields compared to corn planted a month or more ago. Data from Mississippi show up to one third less yield with June planted corn. Irrigation cannot compensate for a short season and potential temperature effects on the crop, and the crop will likely have some dry-down issues at harvest due to lateness of planting.
Where cotton was the planned crop and certain residual herbicides were used, allow at least 6 weeks before attempting to replant to either corn or soybeans. If the field is replanted to corn, wait until crop is emerged and growing well (no obvious herbicide injury) before side-dressing any additional nitrogen. We don’t have much experience with grain sorghum behind some of these residual cotton products and tend to think of sorghum as more sensitive than corn, so sorghum would be the least desirable option in a cotton replant scenario. Before replanting, refer to the labels of any herbicide applied for plant-back restrictions.
