Biological and Agricultural Engineering

Soil and Water Engineering

California’s primary agricultural land is in semiarid or starkly arid zones where precipitation is highly seasonal and often nil during the growing season. Therefore, nearly all food and feed crop production depends on irrigation. Approximately 10 million acres of land are presently irrigated in California. Although California is blessed with abundant precipitation during the winter months, it needs to be stored, then transported to target areas when needed. During the past two decades, however, water development in the state has essentially stopped. As the cumulative impact of formerly developed water resource projects on scenic values, river recreation, fisheries, and wildlife became apparent, the public’s attitude toward new dams became negative. Water application efficiency is therefore a prime consideration of irrigation system design since competition for the state’s water supply by domestic and industrial sectors has increased with population growth. Additionally, increases in energy prices over the past decade have added to the farmer’s irrigation costs whenever pumping is involved. Energy conservation is therefore, a second important consideration in irrigation system design. Another factor of concern is salt build up in the soils. In California, as in other arid regions of the world, salinity is a problem. Judicious application of water is critical for maintaining an acceptable salt concentration in the soil.

Efficient water use on the farm can minimize the quantity of water used and the energy used to pump it. Historically, California has relied heavily on surface application systems. Current research focuses on optimizing reservoir releases and aquifer withdrawals in canal delivery systems, optimizing delivery techniques, and stochastic modeling of temporally and spatially varying soil properties.

Pressurized irrigation includes sprinkle and micro systems. Use of microirrigation has rapidly pro-gressed in California since its introduction about 25 years ago. Over one and a half million acres are presently microirrigated. Student research on pressurized irrigation is oriented toward hardware development and system designs for both agriculture and urban landscapes.

Irrigation inherently affects the environment. Geographic Information Systems (GIS) technology is being developed to assess spatial variability and to provide for more efficient use of water and fertilizer. The entire system must be considered, from the water source to the irrigation return flows. Efficient irrigation results in little water loss and minimal drainage. The water used by the crop, through transpiration and evaporation, is nearly pure, so any minerals (salt) brought into the field by irrigation water
remain in the soil. Leaching of this salt by additional water is required to maintain soil productivity. Through the use of GIS, regional data can readily be transferred, analyzed, and displayed. Our current emphasis is in the correlation of GIS computer structures with regional irrigation/drainage hydrologic models. Our goal is to develop best management practices for integrating agricultural water use with environmental quality.

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Lateral move irrigation machines are very effective in applying water uniformly to a field. Tests have been conducted with various sprinkler hardware on the department’s machine for different wind scenarios.

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Furrow irrigation is commonly used on row crops in California. The goal of this project is to determine spatial and temporal variability of water infiltration and to develop guidelines for improving overall water application efficiency

Geographic information systems (GIS) are being developed to provide systematic approaches to water resource management. In one study, the spatially distributed water, salt, and selenium balances were calculated for the Panoche Water District. Water balance calculations revealed that groundwater is recharged in upslope, undrained regions and discharged as drainage and evaporation in downslope regions. The salt and selenium balances revealed that the geology of soil materials plays a large role in salt and selenium leaching and accumulation rates. Also, salt and selenium accumulation in some regions suggests that anticipated future restrictions on drain water volumes or selenium loads will have a detrimental impact on the region’s agricultural productivity. Costs associated with selenium load are indicated in the left figure, and the figure on the right relates cost associated with excess recharge to the water table

Since the early 1900’s, surface irrigation has remained the predominant application technique in California. The variability of water infiltration is monitored during basin irrigation trials. The goals of many of our studies are to develop procedures for making efficient use of our water resources

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Microirrigation is specially suited for applying reclaimed wastewater. The goal of this project, located at the campus wastewater treatment plant, is to develop disinfection criteria for the prevention of emitter clogging. Studies have been conducted with online emitters and also with drip tape