Cover crops could be an important tool in groundwater management but are being unintentionally disincentivized by groundwater sustainability agencies (GSAs,) according to a new study.
GSAs haven’t done enough analysis or incentivization of cover crops, according to authors of the study. In fact, the study suggests some GSAs are putting a negative spin on the use of cover crops by accounting for their water usage but excluding their water benefits.
Cover crops are planted between crop rows and are not harvested. They are often grasses or legumes and can improve underground water infiltration and storage, soil health and decrease runoff and erosion.
The study points to data that shows cover crops can increase water infiltration by more than 40% and decrease runoff by more than 40%.
The lack of cover crop interest boils down to poor understanding, particularly in the San Joaquin Valley, said Rory Crowley, farmer and one of the contributing authors of the study.
“More than anything, the GSAs are just at a loss for understanding what the true implications are,” said Crowley. “They don’t have a full understanding of what to do with cover crops and how it affects water.”
The study is aimed at helping GSAs deepen understanding of the benefits and processes of cover crops. It was a collaborative effort between many organizations and agencies including the California Department of Food and Agriculture, the University of California Agriculture and Natural Resources and nonprofit Sustainable Conservation.
That information could be especially useful for GSAs building and operating recharge basins to bulk up withered water tables in overpumped aquifers. But, again, Crowley said, the information just hasn’t filtered to the right people.
Crowley grows almonds and walnuts in the Sacramento Valley and has been using cover crops consistently. His land used to suffer from flooding issues and would lose topsoil in the winter. But since implementing cover crops he has seen drastic improvements. The health of the soil and the ecosystem has improved too. Now he helps others grow cover crops.
The Sustainable Groundwater Management Act (SGMA) calls on GSAs to bring groundwater levels back to sustainability by 2040. Water managers are scrambling to enact different strategies to reach that goal.
Whether cover cropping should be a significant strategy within SGMA isn’t yet known, said Crowley. Despite the benefits of cover cropping, there are still knowledge gaps, he admitted.
One aspect that is a bit more complicated is how much water cover crops take away from cash crops.
“That’s kind of a tension point where over the last five or six years some research has been done but more research definitely needs to be done,” said Crowley.
So far, at least with almonds, cover crops have shown negligible water usage in terms of impacts on the cash crop, added Crowley.
The key message right now is that GSAs should dive into this report to better understand cover crops and at the very least, stop unintentionally disincentivizing them, said Crowley.
“I want to see more growers cover cropping. I think it’s clear that cover cropping can improve soil, water, and ecological outcomes. That’s clear in the literature,” said Crowley. “GSAs have to be much better informed about what cover crops are, how to implement them.
Jesse Vad, SJV Water 
