|HIMANSHU, SUSHIL - Asian Institute Of Technology|
|ALE, SRINIVASALU - Texas A&M Agrilife|
|LEWIS, KATIE - Texas A&M University|
|Baumhardt, Roland - Louis|
Submitted to: Frontiers in Sustainable Food Systems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/17/2022
Publication Date: N/A
Interpretive Summary: In the U.S. Southern High Plains (SHP) past field studies of crop rotations of terminated winter wheat followed by dryland cotton have produced conflicting results, which might be because of the trial’s limited sampling of seasonal rainfall conditions. To simulate this rotation under a wider range of rainfall conditions, ARS scientists from Lubbock used wheat and cotton crop simulation models to estimate the effects of winter wheat cover crops on soil water and dryland cotton yields under two common SHP soil types. Winter wheat always reduced soil moisture during the spring, but after it was terminated some soil moisture recovery occurred between termination and cotton planting. Compared to cotton grown in bare ground, cotton yields grown in wheat stubble were increased 50% of the time in one soil, and 67% of the time in the other. But the cotton grown in the wheat stubble almost always led to increased soil moisture at cotton harvest. Like the field studies this work showed that a winter wheat cover crop had a mixed effect on un-irrigated cotton yields, which depended mainly on when and how much it rained. But it also showed that the effects of the wheat stubble on reducing soil evaporation had an important positive effect on conserving soil moisture.
Technical Abstract: Although winter cover crop residue can mitigate the stresses of dryland production in semi-arid regions, cover crops can also reduce soil moisture and cash crop yields. In some field studies of dryland cotton grown after terminated winter wheat in the U.S. Southern High Plains (SHP) and Texas Rolling Plains cotton yields were increased relative to continuous cotton, while others resulted in no significant impact on yields or soil water conservation. These uncertain outcomes may be due to the trial’s limited sampling of seasonal rainfall conditions. To estimate the probabilities of cover crop effects under more representative SHP climate conditions, 294 station-years of crop simulations of terminated winter wheat followed by dryland cotton were conducted. Each station-year’s simulations were repeated under 54 combinations of wheat planting, termination, and cotton planting dates, 2 soil series with different water capacities, and 10 initial soil moisture conditions. When simulations begin with fall soil moisture at field capacity optimal management options for both soils plant wheat early and cotton late, but have different wheat termination dates. Before cotton planting winter cover crop effects are dominated by reduced surface evaporation and increased transpiration, with greater transpiration effects producing decreased column soil moisture (CSM) at wheat termination. Some soil moisture recharge occurs between termination and cotton planting, but cover crops reduce CSM at cotton planting in both soils in ~75% of simulations. Reduced soil evaporation and soil moisture recovery continues after cotton planting, resulting in positive effects on seed cotton yield in 50% of the silty clay loam simulations and in 67% of the fine sandy loam simulations. Gradually reducing initial fall soil moisture in the silty clay loam reduces wheat biomass but increases the incidence of positive effects on seed cotton yields and CSM at cotton planting and harvest. By contrast, drier initial soil moisture in the fine sandy loam had relatively minor yield and CSM effects. In both soils terminated wheat residue led to increased CSM at cotton harvest in at least 75% of the simulations regardless of soil moisture at wheat planting.