Double crop soybean management differs from traditional, full-season management. As double crop soybean planting begins in the Midsouth, we sat down with Angela McClure, Extension soybean and corn specialist with the University of Tennessee to discuss what farmers should keep in mind for the double crop season.
Delta Farm Press: What sort of population density do you recommend for double-cropped beans?
McClure: Double crop planting rate does depend on the equipment being used to plant. For narrow row planters or newer drills that singulate and control seed depth more effectively, we usually plant the more standard rate of 130,000 to 150,000 per acre. When older drills are used where ‘control spill’ seed and depth isn’t controlled well, growers typically plant an additional 15 to 20% more to offset seed loss due to poor placement. There may be other field issues (very heavy residue, hard ground making seed placement difficult) that warrant an increase in planting rate, too.
DFP: Do you recommend a seed treatment?
McClure: I used to say we can skip seed treatments in double crop soybeans, and there are fields planted without any fungicide or insecticide every year. But I have noticed a benefit from at least a fungicide in years like this where June is wet. Seed and seedling rots are reduced in wet fields subjected to warm temps. It might mean the difference between getting enough of a stand to keep versus a replant situation. Soybeans planted in June typically emerge quickly and outgrow thrips and other insects, but usually if a fungicide is going on the seed, it makes sense to put insecticide on as well as often they are a package deal. A seed insecticide buys a few weeks protection from insects that may cause issues later such as three-cornered alfalfa hopper.
DFP: What’s your preferred method of planting and row width for double crop beans?
McClure: Narrow row planter on 20-inch or narrower rows. Coulters sharp enough to cut wheat stubble and trash cleaners that can help shift the worst of the residue off the row to reduce hair pinning. The newer drills are much more effective than we used to see and can do a better job planting into wheat stubble. Narrow rows speed up canopy development and allow rows to lap the middles earlier, reducing weed emergence and conserving moisture which can be important to dryland beans in July.
DFP: What maturity groups do best?
McClure: Maturity group 4 or early 5 would be a stable and consistent double crop bean. Under irrigation, our data suggests a MG 3 is another good option, plus it allows for earlier harvest than a 4 or 5.
DFP: What impact does planting date have on yield potential?
McClure: Delayed planting means there are fewer days to grow and develop yield potential. Soybeans compensate for a shorter growing season by spending less time on each growth stage, which can reduce yield potential. Our highest yielding soybeans are those planted in April or early May based on planting date research and yield contest data. The maturity groups differ somewhat in how they respond to delayed planting. Under dryland conditions yield decline with MG 4 and 5 varieties is less with each day delay in planting compared to MG3 varieties. However, under irrigation, MG 4 and MG 3 varieties have lower rates of yield decline than MG 5 varieties.
DFP: What should growers realistically expect for yield potential and how does that affect inputs, particularly fertilizer?
McClure: Double crop soybean yields under dryland conditions can range from 45 to 55 bushels per acre, depending on rainfall patterns in July and August. I have seen higher yields in years where rain hits just right. Typically, for double crop beans, fertilizer is applied to wheat to cover both wheat and the soybean crop. The University of Tennessee has a separate double crop recommendation to allow for adequate P and K application to wheat that will feed both crops. That recommendation recognizes the reduced yield potential of double crop beans.
DFP: On a different note, there were a lot of early beans planted this year. What are your recommendations for managing early beans as we move throughout the summer? Will the cool May weather have an impact on those early beans?
McClure: We do have more April planted soybeans this year. There were some replants, due to the weather extremes, but overall, our acreage of April planted beans is definitely up. The cool weather in May likely slowed the crop down, possibly delaying bloom by a few days. April planted beans tend to spend the maximum amount of time on each development stage as part of the long growing season and have high yield potential. It is a good idea to stay on top of the crop in order to time foliar fungicides correctly. If you haven’t much experience with early beans, the early pod stage can sneak up on you. Also, early beans tend to be more attractive to insects, as pods and seed begin developing earlier, and scouting will be important to manage potential insect problems.