|MAREK, THOMAS - Texas Agrilife Research|
|Baumhardt, Roland - Louis|
Submitted to: Irrigation Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/8/2016
Publication Date: 9/28/2016
Citation: Marek, G.W., Gowda, P., Marek, T., Baumhardt, R.L., Brauer, D.K. 2016. Modeling long-term water use of cropping rotations in the Texas High Plains using SWAT. Irrigation Science. doi:10.1007/s00271-016-0524-6.
Interpretive Summary: Groundwater resources are finite and becoming increasingly scarce. Crop water use is the major use of rain and irrigation water. Crop rotation strategies that maximize groundwater use extend these resources. In this study, researchers from USDA-ARS (Bushland, TX) and Texas A&M AgriLife Research used the SWAT model and long-term weather data to characterize irrigation requirements of several crop rotations used in the Texas High Plains. Results may serve as a decision tool for producers considering alternate crop rotation strategies by providing irrigation requirements for comparison to known irrigation capacities.
Technical Abstract: The Ogalalla Aquifer is used to supplement insufficient precipitation for agricultural production in the semi-arid Texas High Plains. However, decades of pumping combined with minimal recharge has resulted in decreased well capacity in most areas. The saturated thickness of the aquifer generally decreases in a southward gradient effectively dividing the Texas High Plains into two agricultural production regions. The Southern High Plains (SHP) region is primarily a cotton producing region while the Northern High Plains (NHP) produces a large percentage of corn, wheat, and more recently forages. The planting of winter wheat for grazing or grain production is often a critical management decision particularly in limited irrigation scenarios. We used a calibrated Soil and Water Assessment Tool (SWAT) model to compare simulated yields, total crop water use, and required irrigation for crop rotations of Texas High Plains using measured long-term (90 years) historical weather data. SHP crop rotations included continuous cotton, corn-cotton, grain sorghum-cotton, and cotton-winter wheat. Northern High Plains (NHP) rotations consisted of continuous corn, corn-winter wheat, and the corn-cotton rotation common to both regions. Each rotation designated other than continuous was modeled with alternating crops being planted in the first year of simulation resulting in a total number of ten simulation. Simulated average yields approximated those of established crop production functions although yield range varied considerably, particularly for cotton. The staggered starting crop rotation approach illustrated the inter-annual variation in rainfall and its effect on required supplemental irrigation. Winter wheat yields benefited from above average rainfall during the fall and winter months. A workaround for a limitation of the auto irrigate function in SWAT to be suspended during overwinter crops was used. Summary statistics for crop yield, in-season crop water use, and irrigation were presented for each rotation. Rainfall probability statistics coupled with rotation-specific irrigation requirements may serve as a decision support tool for producers considering alternate crop rotation strategies by providing realistic irrigation requirements for comparison to known irrigation capacities.