WATER RESOURCES RESEARCH GRANT PROPOSAL
Project ID: 2004AZ52B
Title: Controlling Salt Accumulation to Enhance Sustainability of Subsurface Drip Irrigation
Project Type: Research
Focus Categories: Water Use, Agriculture, Solute Transport
Keywords: water conservation, irrigation
Start Date: 03/01/2004
End Date: 02/28/2005
Federal Funds: $11,933
Non-Federal Matching Funds: $34,237
Congressional District: 8
Thomas L. Thompson
Arthur W. Warrick
Subsurface drip irrigation (SDI) is a highly efficient means of water and nutrient delivery for crops that is currently employed on 1-2% of Arizona’s irrigated cropland. SDI is particularly suited for production of high value crops because its use often results in increased yield and quality, reduced chemical use, and greatly enhanced flexibility for field operations, such as harvest. Adoption of SDI represents a considerable capital investment for individual growers. Yet, increased adoption of SDI will be vital if gains in water use efficiency of agriculture, Arizona’s largest user of water, are to be realized. Adoption of SDI for irrigation of annual crops has been slow for several reasons. Among them are doubts regarding the sustainability of SDI systems, particularly with regard to salt accumulation in soils. All irrigation waters contain dissolved salts; therefore introduction of salts is inevitable with irrigation. One disadvantage of SDI is that it often results in high salt concentrations near the soil surface, inhibiting or preventing the growth of salt-sensitive high-value vegetable crops.
Growers who use SDI, particularly with vegetable crops, may need to leach salts periodically with supplemental sprinkler irrigation. Yet, this represents an additional cost that will impact the economic viability of SDI. Development of a method, based upon a mathematical model, that will allow the prediction of the optimum timing and amount of supplemental sprinkler irrigation for SDI systems will be a significant management aid to those growers already using SDI, and should help to allay the doubts of growers considering the adoption of SDI. For each cropped acre converted to SDI, approximately 1.2 million L/yr (1 acre foot) of water will be saved, based on an assumed 25% reduction in total water use, to the benefit of all citizens of Arizona.
The objectives of this project are to 1) identify those factors potentially influencing salt accumulation with SDI, 2) pursue modeling to predict salt accumulation and forecast needed management practices, and 3) validate predictions with data collected in field experiments.
First, we will adopt the HYDRUS-2D solute transport model with appropriate inputs set up to account for SDI system, soil, and environmental factors affecting salt distribution. Model output will predict two-dimensional solute distribution with SDI systems. Second, field experiments will be established at the University of Arizona Maricopa Agricultural Center with different SDI system architectures and water qualities. Two crops will be grown, and solute distribution will be evaluated after each crop. Finally, the data from the field experiment will be used to validate output from the model, and provide the physical basis for adjustment of model parameters. This research project will provide the framework for more extensive validation research on a variety of soil types.