Effects of irrigated agroecosystems: 1. Quantity of soil water and groundwater in the southern High Plains, Texas

Authors

B. R. Scanlon, University of Texas at Austin
R. C. Reedy, University of Texas at AustinFollow
J. B. Gates, University of Nebraska-Lincoln

Document Type

Article

Date of this Version

2010

Citation

Scanlon, B. R., R. C. Reedy, and J. B. Gates (2010), Effects of irrigated agroecosystems: 1. Quantity of soil water and groundwater in the southern High Plains, Texas, Water Resour. Res., 46, W09537, doi:10.1029/2009WR008427.

Comments

Copyright 2010 by the American Geophysical Union. Used by permission.

Abstract

Although irrigated agriculture is the primary consumer of global groundwater resources, information on recharge rates and sustainable irrigation is limited. The study objective was to fingerprint irrigation return flow to quantify percolation/recharge and to estimate sustainable irrigation levels. This paper focuses on water quantity; a companion paper addresses water quality. Soil samples from 13 boreholes drilled beneath irrigated agroecosystems in the southern High Plains were analyzed for matric potential and waterextractable Cl and NO₃. Unsaturated zone pore water beneath irrigated agroecosystems can be fingerprinted by higher matric potentials (wetter soils, median mp: −40 m) and higher NO₃‐N (median 71 mg/L) than beneath natural ecosystems (mp −200 m; NO₃‐N 8.1 mg/L) and by higher Cl (720 mg/L) than beneath rain‐fed agroecosystems (8.4 mg/L). The range in percolation/recharge rates beneath irrigated agroecosystems is 18–97 mm/a (median 41 mm/a; 5% of irrigation + precipitation) and occurs primarily in response to extreme precipitation events. Similarity in percolation/recharge rates beneath irrigated and rain‐fed (4.8–92 mm/a) agroecosystems was unexpected and is attributed to low irrigation applications (median 300 mm/a) and increased crop yield and evapotranspiration in irrigated areas. Regional water table declines are unsustainably large (≥ 30 m over 10,000 km²) in the north and are much lower in the south. Sustainable irrigation in the south would require reduction of the irrigated area from 23% to 9%. Methods developed for quantifying recharge and sustainable irrigation application rates can be applied to groundwater‐fed irrigated areas in semiarid regions globally.