Report: Fallow farmland brings few benefits, but incurs costs
California’s San Joaquin Valley produces an enormous share of the nation’s fruits, nuts and vegetables. But it takes an unsustainable amount of groundwater to do it. New state rules aimed at reducing groundwater use are expected to force up to 20 percent of the valley’s irrigated fields out of production – a blow to farmers and communities.
Now, UC Davis research shows those lands could remain viable if farmers plant winter grain crops. When managed properly, small grains such as wheat, triticale, barley, oats and rye can grow during the cool season, using little irrigation and relying mostly on seasonal rain. The strategy would help farmers keep land productive even during dry winters, without threatening groundwater supplies.
Five years of study from teams led by Mark Lundy and Cameron Pittelkow, both in the Department of Plant Sciences, also show winter grains may help recharge depleted groundwater – even more than taking the land out of production. Their research is part of a new report by the Public Policy Institute of California, or PPIC, which looks at how farmers can comply with the state’s historic Sustainable Groundwater Management Act, passed in 2014.
“We really drilled down into the water use of the winter crops and how that compares to the fallow system,” said Lundy, an associate professor of Cooperative Extension and a co-author on the report. “There’s not been that direct comparison made very frequently or rigorously.”
Small grains can be planted in the fall when it’s cool. They need minimal irrigation to get started, then winter rains take over. If rain is plentiful, farmers can harvest and sell the grain. If not, they can harvest early for animal feed and sell it to nearby dairy and beef operations. During drought, grains offer all the benefits of a winter cover crop, with minimal investment. During wet years, winter crops could even help recharge depleted aquifers.
The report also drew on research by Cooperative Extension specialist Jeff Mitchell and Amélie Gaudin, also in the department.
Best practices plus economic incentives
Over the course of several years, the teams explored different models of cropping systems and how water moves through soil in those systems.
“We looked at how much of that water is being used in ways that are productive for the crop, how much is going to be lost anyway to evaporation and how much going to groundwater,” Lundy explained.
They found that winter crops use only slightly more water than fallowed land. More importantly, while fallowing land reduces the demand on groundwater, it doesn’t recharge groundwater – a common misperception among farmers and rule-makers. Instead, much of the rainfall is lost to evaporation. In addition, fallowed land leads to more dust, pests and weeds, and it traps more heat than acres of winter crops.
In wet years, grain and forage crops shade the soil, reduce exposure to wind and allow water to accumulate from dew. More water sinks in than it would on bare, fallow ground.
In the PPIC report, the scientists offered best-management practices for growing winter grains with little water.
They also advocated for state-funded economic incentives and guidance for farmers to reduce the risks of switching to winter crops and to create and implement tailored farm plans that comply with SGMA restrictions.
That effort, the report concluded, could greatly reduce the loss of productive land as SGMA reductions come into force. That loss is projected to range from 500,000 to 900,000 acres.
“This is an area where many people could win without too much policy effort,” Lundy said.
Funding for the Lundy team’s research came from the Agriculture and Food Research Initiative, part of the United States Department of Agriculture.
Related links
The PPIC report is “SGMA-Ready Crops as a Low-Water Alternative to Fallowing.” Read the report.
The PPIC policy brief is, "Looking at Where Growing a Winter Crop Makes Economic Sense, and How Government Programs Can Support Its Adoption." Read the policy brief.
This article was first published on the UC Davis Department of Plant Sciences news site.