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ARS Home » Pacific West Area » Maricopa, Arizona » U.S. Arid Land Agricultural Research Center » Water Management and Conservation Research » Research » Research Project #437780

Research Project: Quantitative Assessments of Water and Salt Balance for Cropping Systems in Lower Colorado River Irrigation Districts

Location: Water Management and Conservation Research

Project Number: 2020-13660-008-12-S
Project Type: Non-Assistance Cooperative Agreement

Start Date: Jan 1, 2020
End Date: Jun 30, 2021

The project aims to improve water delivery in support of Yuma agricultural productivity and sustainability by quantifying and tracking water use and salt balance across typical Yuma crop production systems and rotations over multiple years. Measurements of germination, growth and yield will be collected and related to the water use and salt balance values. Current estimates of annual water and salt balance in space and time are limited and uncertain. These balances will be greatly improved by collecting water and salt measurements in the field, analyzing samples in the lab, and modeling irrigation practices. Data gathered and analyses conducted will inform the Bureau of Reclamation (Reclamation) on how varying levels of salinity in agricultural water affect agriculture. The project will provide revised crop coefficients for the major crops produced in the Yuma region.

Field Activities: The core activities will be conducted in the field and initiated prior to summer fallow irrigation. Data loggers and sensors monitoring soil salt and soil moisture will remain in the field compiling data until land preparation operations begin for fall produce planting. - Salinity depth and spatial distributions will be measured field-wide using soil conductivity measurements derived from a Geonics EM38 meter. The measurements will be augmented and validated with soil samples. Electromagnetic surveys and soil samples will be collected at the start of a field experiment and after land preparation operations are complete but prior to planting. After planting, the data loggers and will be re-installed before stand establishment of fall-winter crops. -Water deliveries will be quantified using in-flow hydrographs collected during irrigation events. Measurement flumes and data loggers will be deployed. -Evapotranspiration (ET) will be continuously logged at hourly time steps at two locations through crop harvest with two Eddy Covariance (ECV) instruments and one Large Aperture Scintillometer (LAS) instrument. Soil samples will be collected after stand establishment, after thinning water, and at maturity to corroborate the near real tine data collected with the data loggers. Soil samples and EM 38 survey data will then be collected, and the data loggers will be removed for land preparation operations associated with the spring wheat crop. After the spring crop is seeded, the data loggers will be re-installed along the field transects. Inflow hydrographs, infiltrations profiles, evaporation by ECV and LAS, as well as soil water and salt redistributions profiles will be monitored and quantified as described above. The data will be processed using appropriate statistical and mathematical models. -Infiltration will be measured and logged hourly using soil water, soil temperature and soil salinity data during and between irrigation events; these measurements will capture along transect infiltration effects for impounded furrow and basin irrigations relative to inlet and down-stream border locations. -Soil samples will be collected at key time intervals to corroborate sensor data. Salinity Tracking Activities: We will determine if the ion composition of irrigation water remains constant by sampling the source water, water collected in the catch cans, and soil saturated paste extracts. Major cations and anions will be measured. Charge balance will be calculated. Cation ratios will be calculated for all samples. Anions will be quantified using membrane suppression ion chromatography. Cations will be quantified using flame atomic absorption spectrophotometry. Modeling Activities: Surface irrigation data will be analyzed to determine infiltration and hydraulic resistance. Simulations of the irrigation system will be conducted using an unsteady flow model, and the impact of irrigation practices on salt distribution in the soil profile will be characterized. Single crop coefficients (Kc) for commonly grown, economically significant crops in the Yuma area will be developed. Mean crop coefficients are sought.