With decreasing water availability and increased energy costs, there is increased need for alternative management strategies to utilize limited amount of irrigation. Irrigated crop production is a mainstay of agriculture in western Kansas.While crop rotations have been used extensively in many dryland systems, the most common crop grown under irrigation in western Kansas is corn (about 50% of the irrigated acres), often in a continuous corn system. While corn responds well to irrigation, it also requires substantial amounts of water to maximize production. Almost all of the groundwater pumped from the High Plains (Ogallala) Aquifer is used for irrigation (97% of the groundwater pumped in western Kansas in 1995 [Kansas Department of Agriculture, 1997]). In 1995, of 2.46 million acre-ft of water pumped for irrigation in western Kansas, 1.41 million acre-ft (57%) was applied to corn (Kansas Water Office, 1997). This amount of water withdrawal from the aquifer has reduced saturated thickness (in some areas up to 150 ft) and well capacities. Although crops other than corn are grown under irrigation, they have not been grown as extensively because of relatively inexpensive water and a ready market for corn to the livestock feeding industry in the area. The trend in western Kansas during the last decade has been towards increasing acreage of irrigated corn (665,000 acres in 1990 compared to 1.2 million acres in 1999) with corresponding reductions in grain sorghum (326,000 acres in 1990 compared to 104,000 acres in 1999) and winter wheat (692,000 acres in 1990 compared to 498,000 acres in 1999) [Kansas Farm Facts, 1991 and 2000]. Although corn is expected to remain the dominant irrigated grain crop, the need exists to develop strategies to more effectively utilize irrigation water for corn. While there have been increases in irrigated soybean acreage (71,000 acres in 1990 compared to 117,000 acres in 1999), there has been limited research on water use characteristics in western Kansas.
Alternative crop management practices are needed to reduce the amount of irrigation water required while striving to maintain economic returns sufficient for producer (and community) sustainability. The recent increases in natural gas costs (primary source of energy to operate pumps) have intensified the interest in improved economic returns from irrigation water. Cropping systems that rotate a high water using crop (corn) with lower water using crops (e.g. grain sorghum or winter wheat) may result in similar profitability while reducing irrigation water requirements (thereby reducing depletion of the aquifer). To prepare for less water available for irrigation in the future, whether from physical constraints (lower well capacities and declining water tables) or from regulatory limitations, information on crop productivity and profitability with less irrigation water will be beneficial for agricultural sustainability.
Two studies will be initiated under sprinkler irrigation at the Tribune Unit, Southwest Research-Extension Center near Tribune. The first study will evaluate four different crop rotations with a limited irrigation allocation while the second study will evaluate different irrigation amounts in a four-crop rotation. All crops will be grown no-till while other cultural practices (hybrid selection, fertility practices, weed control, etc.) will be selected to optimize production. All phases of each rotation and water levels will be present each year and replicated four times. All rotations will have annual cropping (no fallow years). The irrigations will be scheduled to supply water at the most critical stress periods for the specific crops. Soil water will be measured at planting, during the growing season, and at harvest in one-ft increments to a depth of 8 ft. Grain yields will be determined by machine harvest. An economic analysis will be performed for each study to determine optimal crop rotations and water allocations. A sensitivity analysis will identify the impact of changes in irrigation costs and grain prices on optimal practices. Study 1 – Irrigated Crop Rotations. The rotations will include 1-, 2-, 3-, and 4-year rotations.The proposed crop rotations are:
A total of 10 treatments. All rotations will be limited to 10 inches of irrigation water annually. However, the amount of irrigation water applied to each crop within a rotation will vary depending upon responsiveness to irrigation. For example, continuous corn will receive the same amount of irrigation each year while more water will be applied to corn than wheat in the corn-wheat rotation. The proposed systems will provide 15 in. to corn in rotation, 10 in. to grain sorghum and soybean, and 5 in. to wheat. Study 2- Limited Irrigation for Summer Crops. Irrigation amounts will be 5, 10, and 15 inches annually. The crops evaluated will be corn, grain sorghum, soybean, and sunflower grown in a 4-yr rotation (a total of 12 treatments). The proposed rotation is corn-sunflower-grain sorghum-soybean (alternating grass and broadleaf crops). The irrigation amounts for a particular plot will remain constant throughout the study, e.g.. a plot receiving 5 inches of water one year when corn is grown will also receive 5 inches in the other years when grain sorghum, sunflower or soybean are grown.
Results of the research will be presented to producers at field tours and during winter production meetings. Extension and research publications will be written at the conclusion of the project.