This study evaluated the potential for subsurface drip irrigation in processing tomato to reduce subsurface drainage, control soil salinity and increase farm profits in areas affected by saline, shallow groundwater. ?Subsurface drip irrigation systems were installed in three fields of fine-textured, salt-affected soil along the West Side of the San Joaquin Valley. No subsurface drainage systems were installed in these fields. Yield and quality of processing tomato were compared with sprinkler irrigation systems. Yields increased 5.4 tons per acre to 10.1 tons per acre in the drip systems with similar amounts of applied water. The solids content of drip-irrigated processing tomato was acceptable. Water-table levels showed that properly managed drip systems could reduce percolation below the root zone, reducing subsurface drainage. Yields of the drip systems were also similar over a range of soil salinity levels.
About 4,000 acres of strawberries are grown in the Santa Maria Valley using drip irrigation. In order to help growers irrigate more effectively, we conducted studies to determine crop evapotranspiration; irrigation system performance; patterns and levels of soil salinity; soil moisture content around drip lines; and irrigation water quality. We also developed canopy growth curves. Results at 13 sampling locations showed maximum canopy coverage of less than 75%. Crop evapotranspiration ranged from 12.2 inches to 15.6 inches. Irrigation system evaluations revealed that most of the distribution uniformities were greater than 80%, considered acceptable. The electrical conductivities of the irrigation water ranged from 1 deciSiemens per meter (dS/m) to 2.36 dS/m; levels over 1 dS/m could result in yield reductions in strawberries. However, 79% of the samples had electrical conductivities equal to or less than 1.5 dS/m. Levels of soil salinity in the vicinity of drip lines ranged from 1 dS/m to 3.5 dS/m. This information can help growers calculate crop water needs and estimate irrigation set times.
California’s energy crisis in 2001 resulted in a state-funded program for testing irrigation pumps and improving pumping plant efficiency, with the goal of reducing energy use in California agriculture. Yet in reality, improving pumping plant efficiency may not actually translate into savings. To reduce electrical energy use, the kilowatt-hours must decrease because of fewer kilowatts or less operating time, or both. In order to evaluate the efficiency of various energy-improving adjustments, we studied several operations at pumping plants in the San Joaquin Valley. These included adjusting impellers, repairing worn pumps, replacing mismatched pumps and using more energy-efficient motors. We found that adjusting or repairing worn pumps may actually increase energy use, unless the operating time of the pumping plant is reduced. Multiple pump tests of a pumping plant are recommended, to help evaluate possible reasons for low efficiency. Pumping plant operators should also obtain the manufacturer’s performance curves to use in the evaluation process.
Processing tomato yields have increased by 53% over the past 35 years, but the current seasonal crop-evapotranspiration requirements that growers use to schedule irrigation are based on 1970s-era data. We updated this data and developed new crop coefficients for processing tomatoes using the Bowen ratio energy balance method in eight commercial fields from 2001 to 2004. Today’s evapotranspiration rates are similar to those of the early 1970s, indicating a substantial increase in water-use efficiency by processing tomatoes during the past 35 years. In addition, we collected data in both furrow- and drip-irrigated fields, but no statistical differences were found between them.