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Timing of Winter Cover Crop Termination to Conserve Soil Moisture

Sarah Light (PI), UCCE Advisor in Sutter/Yuba, with Mallika Nocco (UC Davis/UCANR)

Cover crops are a soil health management practice and are planted in soil that is otherwise fallow. In an annual crop rotation in the Sacramento Valley, cover crops are commonly planted in the fall, grow over the winter, and are terminated in late winter or early spring.  In an annual cropping system, having adequate water in specific parts of the soil profile at specific points of the year is critical for cash crop production. For example, growers utilize conserved soil moisture from winter rainfall to germinate spring-planted direct seeded crops like corn and sunflower, or to establish transplanted crops like processing tomatoes.  Annual crop growers report that the soil is dryer in the seeding or transplant depth following winter cover crops and have expressed concerns with winter cover cropping due to extreme drought conditions. Growers need information about how to manage their cover crops with relation to subsequent crop water needs.

This project builds upon an existing research project that indicates there is depletion of soil water in the top foot of the soil profile, which may affect cash crop establishment in an annual cropping system. However, it is unclear if, to conserve soil moisture for subsequent crop establishment, there is an ideal termination date that can be recommended for the region for all cover crops and all soil types. The objective of this project is to collect observational data that can drive an extension recommendation for the optimum timing of winter cover crop termination to conserve moisture in the top of soil profile for subsequent cash crop establishment.

Four annual crop fields will be identified per year for two years (8 total fields during course of the project).  Fields with different soil textures, and planted into a diversity of cover crop species, will be prioritized. Four tensiometers will be installed per field at 6” and 12” depths (2 sensors per depth), to quantify soil water in the part of the soil profile that is critical for the establishment of the subsequent cash crop.  Sensors will be installed in late fall or early winter and will stay in the ground until the grower decides to terminate the cover crop per their standard management practice. The data from this project will be evaluated with existing data to see if different cover crop species or soil types impact soil dry down in the late winter and early spring. Improving our understanding of when to terminate a cover crop in a drought year will help growers manage cover crops without negatively impacting their subsequent cash crop. The benefits of this project are: the opportunity to improve our understanding on water considerations in winter cover crop management in an annual cropping system; the dissemination of research based extension resources on timing cover crop termination to conserve soil moisture for the subsequent cash crop; reducing the risk to farmers of needing to use additional, unplanned water, for cash crop establishment will help our California farms stay profitable and productive in the long term.