Thursday, May 20, 2010
Drip Increases Yields, much of the time
Numero uno is one of the often poorly-understood concepts about drip irrigation.
There are many scientific studies which indicate that drip irrigation can improve growth and yields. For example, in 1981 T. A. Howell et al surveyed 50 research reports on crops grown with drip irrigation, and concluded: “Where trickle [drip] irrigation was compared with either no irrigation or other water-application methods, yields were equal or better in all cases; and the amounts of water applied were equal or less with only two exceptions.” (As summarized by D. A. Bucks and F. S. Nakayama and A. W. Warrick in “Principles, Practices, and Potentialities of Trickle (Drip) Irrigation,” Advances in Irrigation, Vol. 1).
Research in many different climates and states invariably supports the benefits and cost-effectiveness of drip irrigation. Art Gaus, an extension horticulture specialist with the University of Missouri at Columbia, MO, has had a drip system in his personal garden for nine years. One summer, his bush watermelons with plastic mulch and a drip system produced 32 pounds in a four-by-four-foot area, compared with 9–16 pounds in the same area with conventional irrigation. He reckoned a well-timed drip system “could mean a 100% increase in yields; during the droughts of 1980, ’83, and ’84, it meant the difference between having a crop or no crop at all.”
In a study of established pecan trees in Georgia, trees with drip irrigation added had a 51% increase in yields.
Michigan State University has documented a 30% yield increase in vegetable crops with drip irrigation, even in its humid, summer-rain climate.
A study in India in 2002, found that with chilies, water use was down 34–50%, while production was up 33–48%. The researchers attributed this to irrigation that kept the soil moist, not too dry.
A study in New Mexico found amazing differences in yields compared to [respectively] furrow and drip irrigation: 18 pounds versus 30 pounds with cucumbers, 69 to 156 pounds growing Swiss chard, and 64 versus 166 pounds with green beans—to quote a bit of the study. [It is interesting to note that broccoli, Brussels sprouts, and carrots didn’t have any greater yields in the drip irrigation plots. Yet, a study at Oregon State University found a 20% increase in carrots compared to plots with sprinklers.]
To be fair, the benefits of drip irrigation are not confirmed across the board in agricultural studies. There are a number of studies which show it to be less beneficial than sprinklers, especially with perennial and tree crops. One such example is found in a paper entitled “Growth and Yield of Rabbiteye Blueberry as Affected by Orchard Floor Management Practices and Irrigation Geometry,” by K. D. Patten et al. in The Society, September 1989, Journal of the American Society for Horticultural Science, Vol. 114 (5) pg. 724-728. This study found that 360-degree sprinklers created better plant establishment and growth than either one emitter or two emitters per shrub. This is one of many cases where agricultural limitations (such as having to keep the area between tree rows free of tubing and emitters so tractors can mow or disc) greatly restrict both the number of emitters which can be used and their placement. In my drip-irrigation book (Drip Irrigation for Every Landscape and All Climates, 2nd Edition, Metamorphic Press, 2009), I very specifically recommend that emitters be placed equidistant throughout the entire root zone—which would include the area equivalent to that between the rows. The results in the abovementioned study are only to be expected when a dramatically reduced proportion of the root zone is watered by a mere emitter or two.
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Let me know what you think. Visit my web site (www.robertkourik.com) to learn about my new book on drip irrigation and other gardening books. Thanks, Robert