Estimated Farm Level Benefits of Improved Irrigation Efficiency
J. G. Lee, R. D. Lacewell, J. R. Ellis, D. R. Reneau
There are about 15 million acres of cropland in the U.S. that are irrigated from aquifers which are incurring declining water levels (sloggett). This is primarily in the Great Plains Region where irrigation water is pumped from the Ogallala Aquifer. Mining from the aquifer is estimated at 14 million acre feet per year (Frederick and Hanson). The declining groundwater supply increases pumping lift and reduces well yields.
Concurrently, there has been a dramatic increase in the cost of energy for pumping since 1973. For example, in the Trans Pecos Region of Texas, natural gas prices increased 450% from 1972 to 1975. Energy has become one of the most important factors in irrigated crop production. A 1975 study showed that 53% of the total variable costs of producing corn in the Great Plains was energy related (Skold).
The sensitivity of irrigated agriculture to increased fuel costs and declining groundwater levels has provided incentives for irrigated farmers to investigate alternative crop rotations and opportunities to improve irrigation water pumping and distributional efficiencies. The emphasis of this report is to estimate the value to an irrigated farmer on the Texas High Plains of improving irrigation water distribution efficiency.
One means of improving the water use efficiency is to implement water conserving techniques. The main purpose of these techniques is to maximize crop production by minimizing the amount of water lost through the production systems. The major sources of water loss in a crop production system are runoff, percolation, and evaporation. Examples of water conserving techniques include terracing, furrow dams, reduced tillage, and crop rotations. In addition, improved irrigation application techniques can enhance the efficiency of water used for irrigation in the region. On-farm irrigation efficiency statewide for Texas has been estimated between 60 and 708 (Wyatt,1981). The implementation of advanced irrigation application techniques could potentially increase this efficiency up to 98% (Lyle & Bordovsky,1980).
Furrow irrigation and sprinkler irrigation are the two major irrigation systems currently in use. Techniques designed to improve furrow efficiency include alternate furrow irrigation, furrow diking, and surge flow. Alternate furrow irrigation improves the timeliness of irrigation applications and increases lateral water movement thereby reducing deep percolation losses. Alternate furrow irrigation can be used with furrow diking or row dams on non-irrigated furrows to reduce rainfall runoff and soil erosion. The surge flow technique delivers large surges of water into the furrow on an intermittent cycle to reduce percolation losses at the upper end of the field.
Sprinkler irrigation is the second major distribution system used for crop production primarily on mixed and sandy soils in the region. The use of these systems have increased tremendously over the past 25 years. This growth in the use of sprinkler irrigation systems is reflected in the increase for Texas from 668 thousand acres in 1958 to 2.2 million acres in 1979 (Texas Department of Water Resources). With the rapid rise in the relative price of energy during the 1970's, the emphasis of improving sprinkler efficiency has focused on both reducing their energy requirements and decreasing the amount of water lost through evaporation.
One system which has been developed to meet these needs is the LEPA system or Low Energy Precision Application system (Lyle and Bordovsky,1980). This system operates by distributing water through drop tubes and low pressure emitters directly into the furrow as opposed to high pressure systems which utilize overhead sprinklers to distribute the water. In field trials of the LEPA system, measured application and distribution efficiencies averaged 98% and 96% respectively (Lyle et al., 1981).