Construction and Evaluation of Variable-Rate LEPA Irrigation Systems

Issue: Improving agricultural water use efficiency is essential for maintaining the agricultural economy of Texas. Within the same field, crops often require different quantities of irrigation due to variations in soil texture, depth of soil, and the effect of topography on rainfall runoff. For instance, crops located in low laying portions of a field may benefit, or suffer, from rainfall runoff coming from areas of higher elevation. Water use efficiencies at various locations in the same field also differ due to relationships among soil chemical properties, pest infestations, and crop production practices. For example, a pathogen-infested soil capable of supporting cotton yields of only 700 pounds of lint per acre greatly diminishes the value of all inputs when they are applied at rates to achieve 1000 pounds of lint per acre. The appropriate distribution of irrigation, based on one or a combination of measurable characteristics within a field would better utilize both rainfall and irrigation water and help maintain the agricultural economy in the state.

What has been done/discovered: The first variable-rate (VR) center pivot that incorporates the water conserving LEPA irrigation method has been constructed. Spans 6, 7, and 8 of a pivot at the Research and Extension Center at Halfway/Helms were modified to dispense different water quantities along the pivot lateral based on pivot position and previously determined application map. The hydraulic and control components of the VR system were evaluated in July and August of 2001. Preliminary field evaluations comparing VR to uniform rate water application on cotton were conducted with different water treatments beginning in August. An additional VR section (span 5) has since been installed bringing the total VR area to 90 acres.

Impact: The development of this system will allow water conservation and economic evaluations of variable-rate irrigation on the Texas High Plains. Future experiments will provide the methodology for precise water placement within a field so that supplemental irrigation will bring the absolute greatest return while fully utilizing rainfall. An additional benefit is the potential site-specific placement of agricultural chemicals thereby improving their efficiency and reducing environmental risk. Use of variable-rate irrigation systems could impact over 3 million irrigated acres in Texas.

Funding Sources: TAES Precision Agriculture Initiative, Cotton Incorporated, High Plains Underground Water Conservation District No. 1

Contact:
James Bordovsky
Research Scientist and Agricultural Engineer
Research & Extension Center - Lubbock
Texas A&M Agriculture Program
Phone: 806 889 3315
Fax: 806 296 9528
j-bordovsky@tamu.edu
http://lubbock.tamu.edu