Sudangrass studied as cover crop and soil nutrient

By Bob Johnson

Sudangrass is drawing interest as a cover crop that could help answer a variety of soil-quality and water-use issues in different regions of the state.

Planted late in the fall, it produces limited biomass during the cold months in the Central Coast region. This could help growers on high value coastal land incorporate their cover crop quickly enough to meet demanding cash crop schedules.

U.S. Department of Agriculture researchers are including sudangrass in their study of rotation alternatives to suppress soil-borne vegetable disease pathogens.

In the desert, the University of California Cooperative Extension is collaborating with growers to learn if deficit-irrigated sudangrass could improve soil quality while helping the region’s water challenges.

Sudangrass has long held an appeal as a resilient plant that can survive under unusually hot and dry conditions.

Ali Montazar, UCCE farm advisor for Imperial, Riverside and San Diego counties, said sudangrass “used to be a very well-adopted summer forage crop” in the Imperial Valley, with an average of 45,000 acres planted a year.

Now, amid pressures to conserve water supplies from the Colorado River, Montazar said growers have sharply cut back on sudangrass. While farmers in the desert used to grow sudangrass as a forage crop, acreage has declined by 60% since 2019.

Montazar said it could still serve as a low-water cover crop, even though he acknowledged that “cover crop is not a common practice in the desert region.”

He is studying planting sudangrass, germinating it and seeing how much it helps soil quality without irrigation.

“If we eliminate sudangrass as a forage summer crop, let’s plant sudangrass as cover crop and germinate it with a minimum water and leave it alone over the summer,” Montazar said.

“We can still take advantage of this crop as a soil-health practice and conserve a decent amount of water,” he added. “We will try to document its benefits on soil improvements and the impact on leafy-greens growth after the summer.”

Montazar told the 2024 California Leafy Greens Research Conference in Pismo Beach that he is partnering in the study with an Imperial Valley farmer who is using sudangrass as a cover crop.

“I see some promises, but more data is needed,” said Montazar, who has shared first-year study results with the Imperial County Farm Bureau and local growers.

In another ongoing study, USDA research plant pathologist Nicholas LeBlanc is comparing sudangrass, broccoli and radish residue with compost in their ability to suppress fusarium pathogens in the soil.

“We don’t know if green manures are better than compost at disease suppression in leafy greens,” LeBlanc said, noting that different pathogens and diseases “seem to respond to these treatments in different ways.”

Earlier this year, LeBlanc co-authored an article in the journal Microbial Ecology on study results showing that compost can be an effective tool against soil-borne diseases. The report concluded that use of compost can “reduce the activity of common plant pathogenic fungi in soil and suppress diseases they cause on plants.”

In the Central Coast region, UCCE irrigation and water resources farm advisor Michael Cahn is studying whether sudangrass and sorghum-sudangrass could serve as cover crops that can be managed more easily than higher biomass cereal and legume alternatives.

About 5% of the ground in the Salinas Valley is cover cropped every year.

During atmospheric river storms that have become more common, the bare ground is subject to flooding, nitrate runoff and erosion.

A disincentive for vegetable growers to plant cover crops is the difficulty incorporating the biomass in time for spring planting.

Cahn’s study measures the ability of sudangrass to sequester nitrates left in the soil after vegetable crops to stabilize the soil, add biomass and prevent erosion.

(Bob Johnson is a reporter in Monterey County. He may be contacted at bjohn11135@gmail.com.)