Impacts of winter cover cropping on soil moisture and evapotranspiration in California's specialty crop fields may be minimal during winter months

Abstract

As fresh water supplies become more unreliable, variable and expensive, the water-related implications of sustainable agriculture practices such as cover cropping are drawing increasing attention from California's agricultural communities. However, the adoption of winter cover cropping remains limited among specialty crop growers who face uncertainty regarding the water use of this practice. To investigate how winter cover crops affect soil water and evapotranspiration on farm fields, we studied three systems that span climatic and farming conditions in California's Central Valley: processing tomato fields with cover crop, almond orchards with cover crop, and almond orchards with native vegetation. From 2016 to 2019, we collected soil moisture data (3 years of neutron hydroprobe and gravimetric tests at 10 field sites) and evapotranspiration measurements (2 years at two of 10 sites) in winter cover cropped and control (clean-cultivated, bare ground) plots during winter months. Generally, there were not significant differences in soil moisture between cover cropped and control fields throughout or at the end of the winter seasons, while evapo-transpirative losses due to winter cover crops were negligible relative to clean-cultivated soil. Our results suggest that winter cover crops in the Central Valley may break even in terms of actual consumptive water use. California growers of high-value specialty crops can likely adopt winter cover cropping without altering their irrigation plans and management practices.

Assessing the influence of cover crop on soil water dynamics using soil moisture measurements and hydrus‐1D simulations

“…However, recently DeVincentis et al. (2022) reported that there were negligible differences in the actual ET from November 2017 to February 2018 from a field with CC and a clean‐cultivated field (NCC) at two locations in California with different amounts of winter rainfall. In addition, Sharma et al.…”

The Potential of Cover Crops for Weed Management: A Sole Tool or Component of an Integrated Weed Management System?

“…In fact, one of the reasons for the low adoption of cover crop systems in semi-arid regions, such as in California, has been cited as water use by cover crops that reduce moisture availability to the cash crop during the growing season [ 7 ]. However, recent studies have reported that this may not always be the case [ 8 ]. Nevertheless, cover crop benefits may outweigh some of these anomalies in various cropping systems globally.…”

How does building healthy soils impact sustainable use of water resources in irrigated agriculture?

“…Studies are also needed on the potential trade-offs of cover cropping and its effect on the water balance in semiarid regions (Mitchell et al, 2015). For example, some studies have found that both percolation and water storage were reduced under cover cropping (Gabriel et al, 2012;Ward et al, 2012;Mitchell et al, 2015;Meyer et al, 2019), while others show no or little effect (DeVincentis et al, 2022). Several factors will influence outcomes for the water balance, such as the termination timing of the cover crop prior to the cash crop growing season (Alonso-Ayuso et al, 2018), the type of cover crop (or mixture of cover crops; Nielsen and Vigil, 2005), the balance between cover crop transpiration versus improvements to soil physical properties that increase water capture, and then provisioning during the cash crop season and weather (Mitchell et al, 2015;Jones et al, 2020).…”

“…Since green water accounts for a relatively small proportion of crop water use in irrigated Mediterranean systems (Devine and O'Geen, 2019), it is unclear how important increasing green water availability is relative to other mechanisms by which soil health could impact water provisioning and sustainable water use. How soil health practices impact the soil water balance in such systems must also be considered, for instance, whether ET from cover cropping depletes green water for subsequent crops (DeVincentis et al, 2022). With climate change expected to bring even starker contrasts between wet and dry seasons in Mediterranean regions (Nunes et al, 2019), and urbanization and population growth increasing competition for blue water supplies (Nouri et al, 2019a) scoping the role of soil health management for water conservation is essential for policymaking.…”