Soybean Crop Update and Replant Decisions

Trent Irby, Extension Soybean Specialist
By Trent Irby, Extension Soybean Specialist and Bobby Golden, Agronomist, Delta REC, Mississippi State University June 13, 2014 10:58

According to the USDA National Agricultural Statistics Service in Mississippi, 89% of the soybean acreage is planted as of the week ending June 8, 2014. At this time, 82% of the crop is emerged. The remaining acres to be planted will mostly consist of double-crop soybean behind wheat. At this time, Mississippi’s soybean crop ranges from still in the bag to R3.

This planting season has been full of challenges with respect to the weather. We have seen some replanting due to heavy rain and/or herbicide injury earlier this season. Now, after most of the state has received large amounts of rain over the last 14 days, with some areas receiving 10+ inches, there will be some additional acres that will require replanting.

The decision to replant is difficult and can best be addressed on a field by field basis. Generally speaking, the total plant population should be addressed first. In other words, take stand counts from several areas within the field and calculate the estimated plant population per acre. In many cases, yield loss may not be observed for final populations at or above 75,000 healthy plants per acre.

Next, determine whether or not the existing population is fairly uniform, or if there are large skips in a row or blank areas within the field. If there is a fairly uniform stand, even at the low population listed above, replanting may not be necessary. However, if there are large skips within a row or blank areas across the field, it is possible that replanting is the best option. Areas with thin stands can become problematic later in the growing season due to increased weed or insect pressure.

Given that we are now in the middle of June, the question with replanting becomes what maturity group to use. Historically, later maturing, determinate varieties have been selected for planting during this time frame. Recent research suggests, however, that planting a maturity group IV variety (4.6 – 4.9 relative maturity) will result in similar yields as maturity group V varieties planted during this late window, particularly in an irrigated system. Also, a late group IV planted during the middle of June will be ready for harvest several days earlier compared to an early to mid group V. With respect to specific variety selection within this late maturity group IV range, choose a proven variety that is available to you at this time.

If replanting is unavoidable, consider your options for terminating the existing stand. Failure to remove the existing plants could cause problems such as competition between the old and new crop as well as a difference in maturity. Having a difference in maturity of the two interplanted crops may cause issues at harvest. If the decision is made to stay with the existing stand, take extra precaution to protect the plants that you have as any further loss in population may have negative impacts on yield.

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Trent Irby, Extension Soybean Specialist
By Trent Irby, Extension Soybean Specialist and Bobby Golden, Agronomist, Delta REC, Mississippi State University June 13, 2014 10:58
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