Due to severe water shortages, rice acres planted in California plummeted by 37% from 2021 to 2022, according to numbers released recently by the U.S. Department of Agriculture's National Agricultural Statistics Service. But now, thanks to University of California researchers, growers have a new tool they could potentially use to cope with droughts and other environmental and socioeconomic changes.

A crop rotation calculator provides farmers in the Sacramento Valley – where 97% of California rice is grown – with projections on the economic impacts of transitioning their fields from rice into four less water-intensive crops: dry beans, safflower, sunflower or tomato.

The tool represents an initial attempt to address the dearth of research on rice crop rotation in California, while giving growers much-needed, science-backed data on whether the practice would make financial sense for their farms.

“I believe more rice growers could benefit from the many advantages of crop rotation, and this new tool is an excellent first step by the UC to help growers look into making such a transition,” said George Tibbitts, a Colusa County rice farmer.

Funded in part by the USDA National Institute of Food and Agriculture, through the Western Integrated Pest Management Center, the calculator is a collaborative effort of UC Agriculture and Natural Resources, UC Integrated Pest Management and UC Davis to fill a major gap in rice research.

“I do think there are people who would have tried rotational crops in the past, but it's just so unknown, we didn't have anything we could give them and be like, ‘Hey, this is the recommended crop for your area,'” said Whitney Brim-DeForest, UC Cooperative Extension rice advisor. “This tool gives them some preliminary data they can use to make a more informed decision.”

 

 

Crop rotation a potential boon to growers, environment

UC Davis doctoral student Sara Rosenberg and Brim-DeForest, alongside other members of the UC rice research team, surveyed California rice growers in 2020 on their experiences with and perceptions of crop rotation. Although the practice is rare in the Sacramento Valley (only an estimated 10% of rice acreage is under rotation), some farmers reported benefits that could be crucial in a water-scarce future.

“From having conversations with growers who do rotate, one of the biggest benefits they describe is their flexibility in times of drought, where they can keep producing on their land when there isn't enough water to grow rice,” said Rosenberg, noting that crop rotation could be one option in a “toolbox” of strategies that growers also use to manage fertilizer price shocks, herbicide resistance and other challenges.

 

During the ongoing drought that caused about half of California's rice acreage to go fallow in 2022, Tibbitts said his water district was only able to allocate 10% of his usual allotment.

“With such a limited supply, it would have been tough to grow even one field of rice,” he said. “But it was enough water so that we could rent two of our fields to a tomato grower – tomatoes under drip irrigation use much less water than a flooded field of rice. We were also able to grow one field of sunflowers, which doesn't need any irrigation at all if you can plant the seeds into existing moisture in the early spring.”

While drought is one motivating factor to rotate crops, Tibbitts said that on principle he avoids planting all his acreage in rice and “not have all (his) eggs in one basket.”

“My primary motivation for rotating into and out of rice has been to help with weed and disease control,” he added. “Crop rotation is a primary tool of IPM (integrated pest management), and I feel it has helped me greatly over the years.”

According to Brim-DeForest, rotating cropping systems can allow for the use of different weed control tools, such as different herbicide modes of action, and different cultural controls such as tillage, reducing the chances of selecting for herbicide-resistant weeds – an increasingly pervasive issue in rice systems.

Rosenberg noted that, in some situations – and depending on the crops in rotation – the practice can also disrupt the life cycles of insects and diseases and potentially improve soil structure and increase nutrient cycling and uptake, which may lead to a reduction in inputs such as fertilizer.

More research on crop diversification needed in rice systems

The benefits of crop rotation for California rice growers are largely theoretical and anecdotal, however, so the UC rice team is looking to add evidence-based grounding through a variety of studies – from looking at long-term effects on soil health indicators to testing various cover crops (which may deliver some benefits of diversification, similar to those of rotation).

“In California, there is no quantitative data on crop rotation in rice,” said Brim-DeForest. “You'd think after a hundred and some odd years (of UC agricultural research), all the research would have been done, but, no – there's tons still to do.”

 

Through interviews with Sacramento Valley growers, researchers found that cost was frequently mentioned as a barrier to trying crop rotation, along with incompatible soil conditions and a lack of equipment, knowledge and experience.

To help clarify those economic uncertainties, the new calculator tool allows growers to enter baseline information specific to their circumstances – whether they rent or own their own land, whether they contract out the work to plant the rotational crop, and other factors. The calculator then generates potential costs and benefits of staying in rice versus rotating to dry beans, safflower, sunflower or tomato, during the first year and in an “average” year for those crops.

The upfront costs of rotation during “year one” can be daunting. Therefore, the tool only focuses on a short-term profitability perspective. Researchers are currently working on longer term modeling for crop rotation – incorporating the possibility of reduced herbicide use over time, and under different crop yield scenarios, for example – that could significantly change the growers' calculus.

“You could actually be profitable in the long term, whereas this first, short glimpse is showing you a negative,” said Rosenberg.

In addition, thanks to collaboration with the UC IPM team, the rice rotation calculator is an evolving tool that will be continually improved based on user feedback and additional data. Brim-DeForest also said that it could be adapted to other cropping systems – for example, alfalfa going into another rotational crop.

The rice calculator tool can be found at: https://rice-rotation-calculator.ipm.ucanr.edu/.

Other contributors to the project include Bruce Linquist, Luis Espino, Ellen Bruno, Kassim Al-Khatib and Michelle Leinfelder-Miles of UCCE; Cameron Pittelkow of UC Davis; as well as UC IPM team members Chinh Lam, Tunyalee Martin and Hanna Zorlu; and the California rice growers and industry members who participated in the research.