The Way We Irrigate Can and Should Make a Difference

Larry Stein, Ph.D, Extension Horticulturist, Department of Horticultural Sciences, Texas AgriLife Extension Service

Many areas of the state have experienced severe drought conditions during 2010 and 2011. As a consequence, drought management and water use efficiency have once again surfaced as major concerns. If history repeats itself, these concerns will vanish with the next general area-wide rain. The development and implementation of drought management techniques and efficient water use systems will then no longer be a high priority.

Fortunately, the duration of the dry periods and the time required to replenish water supplies, with the ’50s being an exception, have been short. As a result, urban growth and crop productivity have not been seriously impacted. However, as urban population growth continues to increase at a rapid rate and irrigated crop production continues to expand, correspondingly, an accelerated increase in demand on our water supplies is being experienced. Without the development and implementation of drought management and efficient water use techniques, each succeeding drought will have a greater and greater impact on irrigated agriculture and the state municipalities.

Those close to the water issues feel that water use policies and regulations will eventually be developed to insure an adequate water supply for the urban sector. They also feel that the policies and/or regulations will be developed based on emotional and political considerations and not on need or fact. The ability of the agricultural community to influence policy and/or regulations is continuing to decrease and the urban population continues to increase. Although crop producers can do little to curb urban water use or to influence water use regulation, they can have a significant impact on the state water supply and its use. They can do so by adaptating water conserving cultural practices, converting existing irrigation systems in such a manner as to increase water use efficiency, and installing new, more efficient water-use irrigation systems.

Just a few years ago furrow irrigation was the predominant method for supplying supplemental crop water in Texas and overhead high-volume center-point pivot sprinkler systems were a close second. Both of these systems are among the least efficient methods of supplying supplement water to crops. At best, furrow irrigation has a 60% water-use efficiency. With this technique, two-thirds of the field has a full water surface area exposed to evaporation. The addition of surge valves to the conventional furrow irrigation systems have been shown to result in a 10 to 40% water savings. Cost of these conversions is minimal.

The water-use efficiency of overhead high-volume sprinkler systems also falls in the furrow-irrigation efficiency range. These systems have considerable water loss occurring from evaporation and wind drift. Fortunately, most of these high pressure have now been converted to low volume drop systems having the nozzles located approximately 4 feet above the soil surface which has improved efficiency to equal that of surge irrigation (80%) during a normal season.

Conversion of existing center pivots to or purchasing an LEPA system can greatly improve water-use efficiency of the center-pivots concept (up to 95% efficient). With the LEPA system, nozzles are located in the furrow just above the soil surface. Reductions from evaporation and wind drift are achieved. When this concept is used in combination with furrow diking, even greater efficiency can be achieved.

Perhaps the most efficient irrigation system available for use by vegetable growers is drip irrigation in combination with plastic-mulched beds. With this system, water is applied within the row next to plants or to their root systems in frequent low-volume applications. The furrows between the beds remain dry. When the bed surfaces are mulched with plastic, no surface evaporation occurs. In Texas AgriLife Extension Service demonstrations over the past two years, 83 and 74% reductions in water use were found when compared to the conventional furrow irrigation method.

Conversion to or selecting one of the above techniques can make a difference in agricultural water use; not only are yields increased and pumping costs reduced, but, more importantly, they help to conserve our most precious and limited natural resource – WATER. Hopefully irrigated-crop agriculture will take the lead in reducing water use and prevent the need for reallocation to our urban communities as a result of a perceived wasteful use of the state’s limited water supply.

Adapted from the original publication by Frank J. Dainello, PhD, Extension Horticulturist – Commercial Vegetable Crops, Department of Horticultural Sciences, Texas A&M University

Publication updated April 2011

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