Growing cool-season crops could save California water

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Courtesy of Fluence Corporation

Farmers base their decisions on which crops to grow based on a number of factors, including yield, water availability, and return on investment. In California, farmers most often decide to plant crops that thrive between March and October.

Cool-season crops — those grown between October and June — may ultimately use less irrigation water according to new research from the University of California, Davis.

Stephen Kaffka, a UC Davis extension agronomist, explained:

Warm-season crops require a lot of irrigation water. […]They tend to be high-value, but water demanding. Cool season crops have three advantages: the cooler temperatures allow plants to grow without losing as much water through transpiration — like humans’ sweat — as crops that grow during hot weather. There is also less evaporation of moisture from the soil.

And the final and most notable benefit is that this time of year is when California gets most of its rainfall, so there’s less need for irrigation.

Increase in Irrigation

Around the world, irrigation consumes huge amounts of fresh water. Between 1900 and 1950, the area of irrigated land worldwide nearly doubled and it continues to grow. In 2008, irrigation accounted for about 70% of the world’s water consumption. Most of this water originated from surface sources such as rivers.

Demand for water grows in step with demand for food, which is why researchers are investigating a wide range of solutions, including precision drip irrigation, increased water reuse for crop irrigation, and other ways to ensure people can be fed despite growing water scarcity.

Cool-Season Crops

In this project, the UC Davis researchers looked at two cool-season oilseed crops: canola and camelina, plants in the mustard family. Besides being used for oils, plant byproducts are used for livestock feed, and both can be used for biofuels. In the United States, canola is widely grown in the states bordering Canada, and most camelina is grown is Montana.

The U.S. demand for oilseed crops exceeds production. In addition to this motivation to fulfill market demand, farmers can rotate oilseeds with wheat and other cereal crops, which can help provide more weed control options, especially in fields where grassy weeds are a problem.

Selecting Varieties

Making a shift, however, isn’t so simple. There are also many new varieties of canola and camelina. Selecting the best option is a challenge since most camelina varieties are new in the U.S. Growers need recommendations to make the optimal selection for their conditions.

The UC researchers looked at oilseed based on the success of these crops in southern Australia, which has a climate similar to California’s and which relies on rainfall rather than irrigation. The result has been “an extensive and successful canola industry,” according to Kaffka, who adds the methods and varieties used could be successfully applied in California.

Australia’s success is related to the development of varieties for the continent’s abbreviated growing season. These plant varieties flower and set seed before they can be subjected to summer drought and heat stress.

Testing in California

The UC Davis team planted more than 40 varieties of canola and more than 60 types of camelina at locations throughout the state through three growing seasons. They assessed both commercial and experimental varieties and carefully documented all the variables in which each of the test plants was grown, including rainfall amounts and irrigation.

Kaffka says canola could prove a valuable crop. He added:

Canola achieved high yields and seed oil content. […] Using short to mid-season varieties, grown in winter, could help canola become an economically viable crop in California.

Camelina did not offer results that were as definitive, but it could prove a good drought-tolerant alternative for some areas according to the evaluation.

More Research Needed

More research is needed to evaluate a wider variety of both crops. Ideally the team wants to identify more short-season spring varieties. There are also other questions to be answered. Kaffka said:

Agronomic questions that still need research include crop water use, and appropriate irrigation management. We also need research on the effect of diverse planting dates on yield, especially as it relates to soil moisture and temperature.

The research was supported by the University of California’s Division of Agriculture and Natural Resources, and the California Department of Food and Agriculture.

The full results — “Canola and Camelina as New Crop Options for Cool-Season Production in California” — appear in the journal Crop Science.

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