Wheat-Soybean Doublecropping and Soil Properties
A cropping system where wheat is doublecropped [DC] with soybean is used on a significant acreage in the midsouthern U.S. In the 2021-2023 period, there was an estimated average of about 150, 80, and 350 thousand DC acres in Arkansas, Mississippi, and Tennessee, respectively [NASS]. DC acreage in the region fluctuates from year to year based primarily on expected price of the two commodity crops. Reasons for and advantages from DC are presented in a White Paper that is posted on this website.
If DC is practiced at a site, knowledge of the effect of DC management practices on soil properties is important to ensure that a continued DC system is not detrimental to the soil at that site. Results from research conducted at the Univ. of Arkansas sheds some light on this aspect of DC. Links to articles that present these results, along with pertinent points contained in them, follow.
Soil property and soybean yield trends in response to alternative wheat residue management practices in a wheat–soybean, double-crop production system in eastern Arkansas by Amuri et al. [Dec. 2008–content updated Oct. 2015].
• A study was conducted from fall 2001 through fall 2007 on a silt loam soil. The site had been in continuous-till soybean production in previous years.
• The objective of the study was to determine the long-term effects of the below treatments on soybean yield, net economic returns, and soil properties in the top 4 in. of the soil profile.
• Wheat was drill-seeded each fall, and soybean was drill-seeded in early to mid-June each year. Both crops were planted in 7.5-in.-wide rows.
• Treatments each year were 1) tillage [conventional tillage (CT) and no-till (NT)], 2) wheat residue burning [burn and no burn], 3) wheat residue level [low or high, achieved with different nitrogen (N) fertilization rates applied to wheat], and 4) irrigation [irrigated or dryland].
• Soil organic matter [SOM] increased in all treatments over time, and total carbon [TC] increased at a greater rate in the no-burn and high-residue treatments than in the burn and low-residue treatments.
• The increase in SOM and TC [two soil properties related to soil health] over time indicated that silt loam soils used for DC in the region have the potential to accumulate C in the shallow soil depths when wheat residue is not destroyed.
• Finally, NT and no burning of wheat residue have the potential to improve soil quality in a wheat-soybean DC system in the Midsouth.
Long-term management effects on soil properties and yield in a wheat–soybean double-crop system in eastern Arkansas by Norman et al. [Jan. 2016] and Near-surface soil property changes affected by management practices in a long-term, wheat-soybean, double-crop system by Morrison and Brye [Aug. 2021].
• Across the time of these studies [2001-2020], SOM and soil C contents decreased with burning of wheat residue, and conversely, SOM and soil C contents increased with non-burning of wheat residue.
• The results of these studies indicate that irrigation and residue management were responsible for the majority of differences in soil properties near the surface.
• Irrigation was responsible for the greatest differences in soybean yield, SOM content, and the C fraction of SOM.
• The authors concluded that irrigation plays a critical role in SOM accumulation and soil C properties, and that roughly a decade is required before significant positive changes to soil properties and soil C sequestration are realized when DC management practices are changed to those that can potentially enhance them.
• The results from these studies demonstrate that: 1) NT, non-burning of wheat residue, and irrigation of soybeans greatly impact soil properties in the top 4 in. of soil, as well as soybean yield trends over the long term in a DC system; 2) soil bulk density decreased the most in the 0-4 in. soil depth in the NT/no-burn treatment; 3) burning of wheat residue lowered soil nutrient contents; and 4) non-burning of wheat residue resulted in increased SOM, total N, and TC contents in the 0-4 in. soil depth.
All of the above results support the use of NT and non-burning of wheat residue in a wheat-soybean DC production system in the Midsouth to result in the greatest enhancement of soil properties that are related to better soil health.
Composed by Larry G. Heatherly, Oct. 2023, larryh91746@gmail.com