- A new report finds that leaving farm fields bare may waste more water than growing low-water winter crops.
- California’s groundwater law could force up to 900,000 acres of farmland out of full irrigation by the early 2040s.
- Winter grains like wheat and barley need as little as 4 inches of irrigation to produce a marketable crop.
- Researchers say early planting and early harvest are the keys to making low-water cropping work.
- Targeted policy changes at the local level could help farmers make the switch without losing income.
Monday, June 29, 2026 —When California passed its Sustainable Groundwater Management Act in 2014, the goal was straightforward: stop pumping groundwater faster than nature can replace it. In much of the San Joaquin Valley, that pumping has run unchecked for decades, leaving the land literally sinking in some places. To meet the law’s mandate, water agencies have been tightening the screws on how much groundwater farmers can use. The deadline for reaching sustainable levels is the early 2040s.
With less water to go around, many farmers have done what seems logical: leave fields empty. An empty field uses no irrigation water. On paper, it looks like a clean accounting solution. But a report published by the Public Policy Institute of California
in late June 2026 says the math is not that simple.
“Bare fallow fields can cause dust, pest, and heat nuisances,” the report states, “and contrary to common assumptions, they are no more effective at capturing rainfall than appropriately managed crops.”
That last part may surprise people. It surprised researchers, too.
What Really Happens to Rain on a Bare Field.
Here is the problem with empty fields: bare soil is terrible at holding onto rainfall. According to the report, a fallowed field loses between 60 and 90 percent of the rain it receives to simple evaporation before the end of March. That amounts to 4 to 8 inches of water each winter — often the entire season’s rainfall — gone into thin air with nothing to show for it.
Worse, very little of that rainfall actually soaks deep enough to recharge the underground water supply. The report found that groundwater recharge from rain falling on a bare field ranges from roughly one-third of an inch in dry years to about 1.3 inches in the wettest years. That is just 7 to 10 percent of the total rainfall the field receives.
The reason comes down to physics. Bare soil gets pounded by sun and wind. Its surface crusts over. Raindrops hit hard, often bouncing off rather than soaking in. When rain does arrive, it typically comes in small storms that drop less than a tenth of an inch at a time — barely enough to wet the surface, let alone reach the underground aquifer.
In short, a bare field is not a sponge. It is closer to a hot pavement.
A Different Approach: Let Something Grow.
The Public Policy Institute of California report introduces the concept of what it calls “water-limited” or “Sustainable Groundwater Management Act-ready” crops. The idea is to grow plants that survive mostly on rainfall, with only a small shot of supplemental irrigation to get them started. The prime candidates are winter grain and forage crops, including wheat, barley, oats, rye, and triticale.
These are old-fashioned crops, the kind that have been grown in California for generations. They are not glamorous. They do not fetch the prices that almonds, pistachios, or wine grapes command. But they have something those crops do not: they can grow through a California winter on remarkably little water, and there is a ready market for them as animal feed, particularly for the state’s large dairy industry.
The research behind the report draws on more than five years of crop trials and computer modeling, including field experiments conducted in Fresno County during the winters of 2023-24 and 2024-25. The findings point to a practical three-step approach: plant early, apply a small amount of irrigation water at the start of the season to help the crop get established, and harvest the crop early in the spring before warm weather drives up water demand.
“If a crop is minimally irrigated at establishment and harvested as forage,” the report states, “it draws a similar amount of water from the soil as a fallow field.”
That single finding flips the conventional wisdom on its head. Growing a crop, under the right management, does not necessarily use more groundwater than leaving the field empty.
Small Water Investment, Real Returns.
The numbers in the report are worth pausing on. A conventional winter cereal crop in the San Joaquin Valley might need 18 to 20 inches of irrigation water over the growing season. Under the water-limited approach, researchers found that just 4 inches of irrigation applied early in the season — roughly 20 percent of that full amount — was enough to produce a marketable forage crop in both average and dry years.
When planted in mid-October rather than the more typical November-through-January window, crops produced significantly more forage per inch of water used. Earlier planting allows the crop to take full advantage of winter rains before warm spring temperatures arrive and push water demand higher.
The tradeoff is timing. Farmers are asked to plant and spend money on irrigation before they know what kind of winter is coming. In a dry year, yields will be low. The report acknowledges that risk directly and calls on policymakers to help reduce it through crop insurance or reimbursement programs, particularly for years when rainfall falls short.
More Than Just Water Savings.
There are benefits beyond groundwater that the report highlights. A field covered in growing wheat or barley does not send dust clouds rolling across the valley, something bare fields do regularly. Dust from fallowed San Joaquin Valley farmland has become a serious public health issue, linked to Valley Fever and respiratory disease. Research cited in the report also points to a “heat island” effect from bare fields: the exposed dark soil heats up significantly in the sun, raising temperatures in neighboring fields and increasing stress on nearby crops and farm workers.
Winter grain crops also improve the condition of the soil itself, maintaining organic matter and protecting against erosion. And in wet years, fields planted in winter crops may actually capture and store more water than bare ground. Plant roots create channels in the soil, and crop canopies shade the ground surface, reducing evaporation. Both effects improve how efficiently rain soaks in rather than evaporating away.
The report notes that some farmers and water districts are already experimenting with planting winter grain crops in fields used for managed aquifer recharge — a practice where extra water, often from flood flows or storm runoff, is intentionally spread over land to soak into the ground and replenish the aquifer below. Winter crops fit well into this practice because they cost relatively little to establish, and a flooded, sacrificed crop in a wet year can still be a worthwhile trade if it means more water underground.
What Needs to Change at the Policy Level.
The report identifies a significant obstacle: some local groundwater agencies, in trying to enforce water cutbacks, have unintentionally discouraged farmers from growing winter crops by counting even small amounts of crop water use against pumping allowances. Others require bare soil on fallowed land, leaving no room for low-water cropping.
The report calls on groundwater sustainability agencies to update their accounting rules so that modest winter crop water use is not penalized. It also calls for the development of credit systems that recognize the role of winter-cropped fields in capturing and storing rainfall, something the report’s authors call “precipitation credits.”
At the state level, the California Department of Water Resources, the California Department of Conservation, and the State Water Resources Control Board are identified as having a role in providing guidance to local agencies, particularly smaller and under-resourced districts that may lack the staff and research capacity to evaluate these options on their own.
The report is careful to note that no single crop or management approach will work everywhere. Farmers know their own land and their own circumstances best. But the research suggests that for a significant portion of the valley’s farmland currently headed toward bare fallowing, winter grain crops represent a practical, immediately available alternative — one that can keep land productive, keep topsoil in place, support California’s dairy and livestock industries, and protect the groundwater supply all at the same time.
Up to 900,000 acres of San Joaquin Valley farmland could be forced out of full irrigation under the Sustainable Groundwater Management Act if new water supplies are not developed. The report’s authors argue that thoughtful policy and targeted management can put a meaningful portion of that land to productive use, rather than leaving it bare and blowing in the wind.
