Tuesday, November 6, 2007
208-3

Crop Rotations with Limited Irrigation.

Alan Schlegel, Kansas State University, Southwest Res. Ext. Center, 1474 State Highway 96, Tribune, KS 67879, Loyd Stone, Kansas State University - Agronomy, Manhattan, KS 66506, and Troy Dumler, KSU-SW Area Extension, Garden City,, KS 67846.

Limited irrigation research was initiated under sprinkler irrigation in western Kansas at the Tribune Unit, Southwest Research-Extension Center in the spring of 2001. The objectives were to determine the impact of limited irrigation on crop yield, water use, and profitability in several no-till crop rotations. The crop rotations were 1) continuous corn, 2) corn-winter wheat, 3) corn-wheat-grain sorghum, and 4) corn-wheat-grain sorghum-soybean. All rotations were limited to 25 cm of irrigation water annually, but the amount of irrigation water applied to each crop within a rotation varied. The irrigation amounts were 38 cm to corn in 2-, 3-, and 4-yr rotations, 25 cm to grain sorghum and soybean, and 12 cm to wheat. The continuous corn received 25 cm annually. Irrigations were scheduled to supply water at the most critical stress periods for the specific crops and were limited to 38 mm/week. Soil water was measured during the growing season in 30 cm increments to a depth of 240 cm. Grain yields were determined by machine harvest. Averaged across the past 4-yr, continuous corn was the most profitable system primarily because of spring freeze and hail damage to the wheat in the multi-crop rotations. However, the multi-crop rotation may reduce economic risk when the monoculture crop does not perform well. All of the multi-crop rotations had net returns within $50/ha of that of continuous corn so only relatively small changes in prices or yields would be needed for any of the rotations to be more profitable than continuous corn indicating the potential for alternate crop rotations under limited irrigation.