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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 focuses on soil and water quality.

Soil Health

Cover Cropping

With funding from the CDFA Healthy Soils Program, we evaluated a warm-season legume cover crop between winter small grain forage crops compared to a standard dry fallow. From 2018-2020, we assessed soil health properties, greenhouse gas emissions, and forage yield in replicated plots within a commercial field. In this report, we describe the potential for summer cover cropping to improve soil tilth at a time of year when the soil might otherwise be fallowed and dry with no soil cover.

Compost Amendment

We have also received funding from the CDFA Healthy Soils Program to evaluate the potential for compost amendment to improve soil structure and fertility in alfalfa fields. This study will take place from 2020-2023 in replicated plots in a commercial field. We will investigate the effect of two application rates of green waste compost on greenhouse gas emissions; soil structure, fertility, and carbon storage; and alfalfa yield and quality. 


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 downstream flows or seawater intrusion. In this presentation to the State Water Resources Control Board, I described my research in Delta alfalfa, tomato, and grape fields to examine soil salinity profiles and leaching. This fact sheet describes soil salinity management strategies and challenges.

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. In this paper, we review 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. 

Crop Consumptive Use

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. In this 2015-2016 study, we used field-based measurements and remote sensing to develop estimates of crop consumptive use in the Delta, to help inform water management decisions around diversion reporting.