Evaluating on-farm irrigation efficiency across the watershed: A case study of New Mexico's Lower Rio Grande Basin

• On-farm irrigation efficiency values were calculated for several hundred fields.
• The results showed actual ET for majority of fields were lower than potential ET.
• The study showed significant variability in on-farm efficiency.
• The study showed significant potential for water conservation.

Irrigation efficiency is a critical factor in irrigation water management. Irrigation efficiency is used in economic analysis when selecting an irrigation system design, and in irrigation management. It is also used in water rights adjudication and administration. On-farm irrigation efficiency is spatially and temporally variable and measuring irrigation efficiency is time consuming and costly. This paper describes a process to evaluate on-farm irrigation efficiency across the watershed using a combination of remote sensing and ground level measurements. On-farm irrigation efficiency was evaluated for three major crops in New Mexico's Lower Rio Grande Basin (LRG). The results of on-farm irrigation efficiency evaluation of 152 alfalfa fields, 189 pecan fields and 38 cotton fields showed that the average on-farm irrigation efficiency was 64%. However, on-farm irrigation efficiency values ranged from 11% to 95%. Accounting for delivery efficiency of 54%, the overall district efficiency was calculated as 35%. The study shows significant potential for improving irrigation efficiency in the LRG watershed; however, the inefficiency of the system is a major factor in recharging and sustaining the local aquifer. Significant improvement in on-farm and delivery efficiency can potentially change the hydrologic balance and result in depletion of the historically stable groundwater of the Mesilla Bolson.