Soil and Water Resources
Agriculture has a long history in the Delta, but Delta growers face unique challenges that bridge the agricultural and environmental sciences. Understanding soil and water resources in the Delta is critical to understanding Delta agriculture. The soils were formed from tule marsh decomposition, and the surface water used for irrigation is from upstream runoff interfacing with seawater. While half of the state’s runoff exits through the Delta – making the Delta appear water rich – the quality of the water is often degraded by the time it reaches the Delta. My research and extension program in resource management has a focus on soil quality, with a particular emphasis on salinity. I work collaboratively with others on projects related to water resources.
In Delta cropping systems, soil salinity varies based on surface water quality, depth to and quality of the groundwater, irrigation methods, and volume of winter rainfall. Salinity challenges Delta farmers’ ability to grow crops, especially under conditions of reduced water flows or high surface water salinity. I have conducted research in Delta alfalfa, tomato, and grapes fields to gain a better understanding for soil salinity profiles and leaching.
With funding from the CDFA Healthy Soils Program, we are evaluating a warm-season, annual legume cover crop (Vigna unguiculata cv. ‘Red Ripper’) between winter wheat rotations compared with a standard dry fallow. We are assessing soil health properties, greenhouse gas emissions, and grain yield in replicated plots within a commercial field. Cover cropping is not a typical practice in the annual crop rotations of the Delta region, and summer cover cropping is particularly rare. Summer cover cropping with a legume has the potential to improve soil tilth at a time of year when the soil would otherwise be fallowed. A preliminary report describes the first two years of this three-year project.
Select Presentations on Soil and Water Resource Management
Drought and the Delta
The precipitation and duration of the 2012-2016 drought was similar to those of past droughts, but what made 2012-2016 unique was warmer temperatures and reduced snowpack. We are reviewing how state water resources management impacted the Delta during the 2012-2016 drought, giving particular attention to impacts on public health, saltwater intrusion, preservation of cold water in upstream reservoirs, and protections for endangered species. Stay tuned for the report.
Crop Evapotranspiration in the Delta
With the passage of SB 88, growers are required to measure surface water diversions for agricultural use. The unique hydrology of the Delta makes these measurements difficult. The 2015-2016 Delta crop evapotranspiration study, which estimated crop consumptive use using field-based and modeling methods, had the following conclusions:
- Crop evapotranspiration was approximately 1,400 thousand acre-feet (TAF) in each year.
- Alfalfa, corn, and pasture are the three largest crops by area and accounted for nearly 60 percent of crop evapotranspiration in each year.
- Non-agricultural land uses, such as native riparian and floating vegetation, have a higher per-acre evapotranspiration than crops, on average. The water use of these vegetation types needs further study.
- Remote sensing-based ET estimates appear to be a cost-effective way to reduce self-reporting of diversions and provide transparency and consistency in ET quantification.