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Comparison of Limited Irrigated vs. Dryland Cropping Systems in the U.S. Great Plains

Norwood, Charles A.
Agronomy journal 1995 v.87 no.4 pp. 737-743
Triticum aestivum, Sorghum bicolor, continuous cropping, crop rotation, fallow, irrigated conditions, dry environmental conditions, crop yield, water use efficiency, grains, Kansas
Irrigated hectares in the Great Plains are being converted to dryland because of the declining water table and increasing energy costs for irrigation. A study was conducted in the central Great Plains near Garden City, KS, from 1989 through 1991 to compare limited-irrigated cropping systems for use on land that would otherwise be converted to dryland. Irrigated continuous winter wheat (L.) and grain sorghum [ (L.) Moench] were compared with the wheat-sorghum-fallow rotation where either one, both, or neither crop was irrigated. Irrigated wheat yields in the rotations averaged 26% more than dryland. Rainfall eliminated any benefits of irrigation on the 1989 and 1990 grain sorghum, but yields in the rotations were increased an average of 168% over dryland in 1991. Average irrigated continuous wheat and sorghum yields were 19 and 8% less than irrigated rotated wheat and sorghum yields, respectively, in 1990 and 1991, but when yields were annualized continuous wheat and sorghum averaged 20 and 59% more than the irrigated rotations. Annualized irrigated rotation yields were similar to dryland in l990, but 68% more in 1991. Irrigating either crop in the rotation produced similar annualized yields, but irrigating both crops increased yield an additional 13%. Irrigation water use efficiencies were highest for the rotated crops, and lowest for the continuous crops. More grain can be produced with very limited irrigation than with dryland systems, but no single system is best for all conditions. Producers with less water should probably irrigate fallow systems, while those with more water can crop more intensely.