Field-scale monitoring of the long-term impact and sustainability of drainage water reuse on the west side of California’s San Joaquin Valley

Authors: Corwin, Dennis

Submitted to: Journal of Environmental Monitoring
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/27/2012
Publication Date: 5/20/2012
Citation: Corwin, D.L. 2012. Field-scale monitoring of the long-term impact and sustainability of drainage water reuse on the west side of California’s San Joaquin Valley. Journal of Environmental Monitoring. 14(6)1576-1596.

Interpretive Summary: Greater urban demand for finite water resources, increased frequency of drought resulting from erratic weather, and increased pressure to reduce drainage water volumes have intensified the need for drainage water reuse in arid and semi-arid agricultural areas. Drainage water reuse would be particularly useful on the west side of California’s San Joaquin Valley (WSJV) where no drainage water disposal outlet exists. To dispose of drainage water evaporation ponds are used, which could remove as much as 34,000 ha of land from productivity in the WSJV. A 12-year study has been developed to determine if the quality and productivity of forage grown on previously low-productivity, saline-sodic soils of the WSJV can be maintained at sufficiently high levels to be sustainable when irrigated with drainage water. A long-term (10 year) evaluation is made of the sustainability of drainage water reuse from the perspective of the impact on soil chemical properties crucial to the soil’s intended use of producing forage for livestock. Results of the evaluation were positive. Drainage water reuse is shown to not only reduce drainage volumes thereby mitigating the need for non-productive evaporation ponds, but an alternative water resource asset becomes available that can be used to economic advantage by reclaiming non-productive saline-sodic soils and bringing them back into agricultural production. However, once irrigation of the reclaimed field is terminated it returns quickly (less than 2 years) to its original saline-sodic condition. California Department of Food and Agriculture, land and water resource managers, producers, extension specialists, and Natural Resource Conservation Service field staff are the beneficiaries of this demonstration of the sustainability of drainage water reuse.

Technical Abstract: Diminishing freshwater resources have brought attention to the reuse of degraded water as a potential water resource rather than as a disposal problem. Drainage water from tile-drained, irrigated agricultural land is degraded water that is often in large supply, but the long-term impact and sustainability of its reuse on soil is unknown. Similarly, nothing is known of the ramifications when the reuse of drainage water is terminated. It is the objective of this study (i) to monitor the long-term impact of drainage water reuse on a marginally productive, saline-sodic, 32.4-ha field located on the west side of California’s productive San Joaquin Valley, (ii) to evaluate its viability and sustainability as a alternative water source, and (iii) to spatially assess what happens to soil when drainage water reuse is terminated. The evaluation of sustainability was based on spatial soils data collected during 10 years of irrigation with drainage water followed by 2 years of no applied irrigation water (only rainfall). Geo-referenced measurements of apparent soil electrical conductivity (ECa) were used to direct soil sampling at 40 sites. Soil physical and chemical analyses of the soil samples were used (i) to characterize the spatial variability of soil properties (i.e., salinity, Se, Na, B, and Mo) identified as critical to the yield and quality of Bermuda grass (Cynodon dactylon (l.) Pers.), which was grown at the field site for livestock consumption, and (ii) to monitor their change during the 12 years of the study. Soil samples were taken at 0.3-m increments to a depth of 1.2 m at each sample site on five separate occasions: August 1999, April 2002, November 2004, August 2009, and May 2011. Drainage water varying in salinity (1.8–16.3 dS m-1), SAR (5.2-52.4), Mo (80–400 µg L-1), and Se (<1–700 µg L-1) was applied to the field from July 2000 to June 2009. Results indicate that salts, Na, Mo, and B were leached from the root zone causing a significant overall improvement in soil quality from 1999 to 2009. Salinity and SAR returned to their originally levels or higher in less than two years after the termination of irrigation, while B and Mo showed significant increases, and pH increased over the 12 years, particularly when drainage water reuse was terminated. Long-term sustainability of drainage water reuse is supported by the results, but once the application of irrigation water is terminated, the field quickly returned to its original saline-sodic condition.