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IRRIGATION

Transition to Dryland Agriculture

Limited Irrigated vs. Dryland Corn

Southwest Res. Ext. Cent., 4500 E. Mary, Garden City, KS 67846

* Corresponding author (cnorwood{at}gcnet.com)

Received for publication March 12, 2001. Corn (Zea mays L.) is grown on more irrigated hectares than any crop in the Great Plains. Much of this area is irrigated from the Ogallala aquifer, which is being depleted. Research was conducted at Garden City, KS, from 1998 through 2000 to compare grain yield and water use of short- and long-season corn hybrids to determine if limited irrigation is a viable alternative to dryland in an area of declining ground water. Corn hybrids having maturities of 104 d (H1) and 116 d (H2) were grown at populations averaging 44000 (P1) and 69000 (P2) plants ha^-1. Treatments were dryland and 150 mm (one irrigation) and 300 mm (two irrigations) of water. When irrigated, H2 yielded most in the two wettest years, but H1 yielded most in the driest year. Average grain yields from dryland, one irrigation, and two irrigations of H1 were 6.38, 8.23, and 8.79 Mg ha^-1, respectively. For H2, yields were 5.75, 9.04, and 9.75 Mg ha^-1, respectively. Grain yield responses from two irrigations did not occur for either hybrid in 1999 or for H1 in 1998. At current pumping costs of about $0.20 mm^-1, it is probably not economically feasible to irrigate more than once unless the corn price exceeds $0.099 kg^-1. Irrigating long-season corn once, given a price of $0.099 kg^-1, will increase profits by $71 ha^-1 more than dryland production and $44 ha^-1 more than with a short-season hybrid. Lower corn prices and/or higher pumping costs will force the conversion of irrigated hectares to dryland.

Abbreviations: H1, 104-d hybrid • H2, 116-d hybrid • IWUE, irrigation water use efficiency • P1 and P2, low and high plant populations, respectively (see text) • WUE, water use efficiency

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