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Maximizing Doublecrop Soybean Yields

Doublecropping refers to the practice of growing two crops in one year. In the southern U.S., this production system usually involves growing winter wheat and soybeans in rotation. However, wheat acreage in the Midsouth has been low in recent years, and was only 4.8% and 3.2% of soybean acres in Arkansas and Mississippi in 2021 (wheat acres in Louisiana were negligible). There were only 215,000 total wheat acres in Arkansas and Mississippi in 2021 even though these two states had the most soybean acres (3,010,000 and 2,190,000, respectively) in the southern U.S. (NASS).

Doublecropping is more prominent in the southeastern (SE) U.S., where wheat acreage in 2021 in Georgia, Kentucky, North Carolina, South Carolina, and Tennessee was 84.6%, 19.6%, 21.2%, 27.0%, and 22.4% of soybean acres, respectively. Total wheat acres in these five states was estimated to be 1,235,000 in 2021, which was 23% of the 5,390,000 soybean acres in those five states (NASS).

Yields of both wheat and soybeans in a doublecrop system are important to those producers who use the system, because those yields coupled with the combined expenses associated with producing both crops will ultimately determine the profitability of the system that uses two crops vs. growing either crop alone. Thus, results from research reported in an article titled “Double-crop soybean management practices for high yield and profitability” (Crop Forage & Turfgrass Mgmt., 2021; https://doi.org/10.1002/cft2:20119) provide important information for producers who practice doublecropping. Pertinent points from that article follow.

•    Doublecrop soybean trials were established at the Research & Extension Center near Princeton, KY (37°10' N latitude) . Studies were conducted for 3 years (2017-2019) on two soil types–a well-drained silt loam, and a moderately well-drained silt loam. A MG 3.5 soybean variety was planted into standing wheat stubble in a no-till system.

•    Six management practices were used in the experiment. They were: 1) seeding rates of 150 (base rate) and 225 thousand/acre; 2) seed treatment with a fungicide + insecticide and non-treated; and 3) application of foliar fungicide and insecticide (Quadris Top and Warrior II) using a separate economic threshold for diseases and insects, or a prophylactic application of both at R3. The baseline or base management treatment was comprised of the lower seeding rate, no seed treatment, and in-season fungicide and insecticide applied at economic thresholds.

•    All treatments were applied to “early” and “normal” soybean plantings that were made following wheat harvested at high (20-22%–early) and low (13-15%–normal) seed moisture contents. The early plantings occurred an average 17 days before the normal plantings (June 9-13 vs. June 21-July 5).

•    In all 3 years, the early planting produced a significantly greater yield than the normal planting. Across the 3 years, average yields were 64.7 and 54.0 bu/acre for the early and normal plantings, respectively. Results indicate that the yield penalty for delayed soybean planting following wheat in a doublecrop system is equal to or greater than that for delayed plantings of monocropped soybean.

•    Across both plantings in all 3 years, the higher seeding rate resulted in significantly greater yield of 6.0 bu/acre.

•    Seed treatment did not increase soybean seed yield, but this was not surprising since seed treatments should be applied to achieve a plant population that will ensure an adequate stand vs. to achieve a yield increase. (A Seed Treatment White Paper on this website presents an example of how seed treatment can be used to allow a reduced seeding rate and still achieve the desired plant population.).

•    The prophylactic pesticide application at R3 resulted in an average 5 bu/acre greater yield than that resulting from pesticide applications applied according to economic thresholds. The prophylactic treatment had less frogeye leaf spot symptoms and less-severe insect infestation than the economic threshold treatment at both 14 and 28 days after treatment.

•    When all treatments were combined into the most intensively managed system (high seeding rate, seed treatment, and application of a foliar fungicide + insecticide at R3), the highest soybean seed yield was produced in all years. However, the greatest likelihood of profitability occurred when soybean was planted early with only the base management practices. In contrast, the high seeding rate provided the greatest positive economic return in the normal planting.

•    These results indicate that: 1) the more intensively managed soybean plantings in the doublecrop system resulted in greater yields but not greater profits; 2) planting early was an effective management strategy for increasing doublecrop soybean yields; and 3) when soybean was planted early, the base treatment of the lower seeding rate, no seed treatment, and foliar pesticides applied according to economic thresholds was profitable most of the time.

Caveats. 1) The “early” planting in this study followed wheat harvested at a higher-than-normal seed moisture content, which would necessarily result in dockage for high-moisture wheat delivered to the elevator, or an added cost of drying. It is not clear if this additional cost was included in the analysis. 2) The profitability from using any of the high intensity management practices applied in this study would depend on both cost of the additional inputs and commodity price received for both the wheat and soybeans. Both of these economic factors will change with each growing season, which means that the results from this study that used a variation in factors should be evaluated for each growing season that will have different input costs and commodity prices for both the wheat and soybeans.

The above results confirm the following about doublecropping. The decision to doublecrop soybeans and wheat is influenced by agronomic factors that include harvest date of the wheat crop (which dictates soybean planting date following wheat harvest), soil moisture status (with no irrigation) for soybean planting and emergence, availability of seed of desired soybean varieties, and economic factors that include the return realized from the wheat crop, expected soybean price, and the expected yield of soybeans following wheat compared to the certain higher yields from ESPS plantings of monocropped soybean in the Midsouth.

For a detailed discussion of doublecropping in the Midsouth that includes the best management practices that should lead to the best results from adoption of this system, click here.

Composed by Larry G. Heatherly, Dec. 2021, larryh91746@gmail.com