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Green and growingBy D. Bruce Bosley Extension Agent/Cropping Systems, Colorado State University Cooperative Extension CSU Researchers are learning more about alfalfa and how drought tolerant it really is. Dr. Neil Hansen and a couple of his graduate students have been conducting limited irrigation research trials on alfalfa at the Northern Water Conservancy District's headquarters in Berthoud, Colo., since early last year. Their findings may be very helpful for farmers who having to limit their irrigation water due to shortages along the South Platte basin. It has long been known that alfalfa produces more on the first cutting than at any time of the summer growing season. Dr. Danny Smith, Colorado State University professor in agronomy, had determined in 1990s studies that it takes about 2.4 inches of water from rainfall and irrigation to produce 1 ton of hay for the first cutting in the spring on alfalfa fields in northeast Colorado. Furthermore, summer hay production took much more water to produce hay: 3.2 inches/ton for second cutting and 4 inches for third cutting. As temperatures cool for the fourth cutting the water needed becomes very efficient again at 2.2 inches/ton, but because the season is shorter than that preceding the first cutting only two thirds as much hay is produced as for first cutting. These relationships between spring and fall versus summer water use efficiency for alfalfa production led Smith to suggest that eliminating summer watering may be a very cost effective way to reduce the requirement for alfalfa irrigation water, as well as cutting some haying operations. Danny's suggestion intrigued Neil Hansen who was hired to continue studying dryland and limited water cropping systems. When Neil had developed a partnership with Northern Water Conservancy District's agronomist the current research project was established. The results of the 2006 alfalfa study gave the following alfalfa yields. Fully irrigated alfalfa receiving 27 inches produced 7.7 tons of dry hay. In comparison Alfalfa which only received 14 inches of irrigation water through the second cutting produced 6.5 tons. Alfalfa receiving only 13 inches and having been watered once after the first cutting and again before the fourth cutting yielded 6.0 tons. The final alfalfa treatment received only 5 inches of water all during the spring before first cutting yielded 4 tons. With about half the water the second and third treatment yielded 84 percent and 78 percent as much hay as the fully irrigated alfalfa during a very hot and dry summer. The treatment receiving less than 20 percent of the fully irrigated one produced half as much hay. What really surprised Hansen was that all of the reduced irrigation treatments had better protein and digestible energy quality factors than the fully irrigated hay. So what happened to these treatment plots through the winter and into this year? With first and second cuttings completed all plots have yielded nearly the same: Over 3 tons on first cutting and two to two and a quarter ton for second cutting. The treatment irrigated through the second cutting last year has yielded slightly more. Finally, Hansen's research assistant graduate students are finding more stems per square foot on the stressed treatments than the fully irrigated treatment. They believe these treatment stands appear healthier as well. The take home message is that it appears that alfalfa is a very drought adapted plant. It's a very tough plant indeed. My question is: Does keeping the crop environment for alfalfa encourage the disease related stand losses? This question is for another study. This research will be expanded to include other grass and grass and alfalfa mixes in the Lower South Platte Irrigated Research project being conducted in the Iliff area starting this fall. Please contact me, Bruce Bosley about these or other cropping systems or natural resource topics at 522-3200, ext. 285 in Sterling or 542-3540 in Fort Morgan. Date: 8/8/07
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