University of California Cooperative Extension researchers have started field trials to analyze the benefits and trade-off of planting cover crops near or within almond production systems.

Trials in Tehama, Merced, and Kern counties are replicating conditions in almond orchards with micro-irrigation systems, according to a UC newsletter. The scientists are watching the performance of two cover crop mixes, different termination dates, weed population shifts, beneficial and plant parasitic nematodes, frost risk, water usage, and other factors.

The trials come as some are urging growers to use flowering plants to improve soil health and strengthen bee populations prior to bloom. “Almond growers have indicated interest in the use of cover crops,” the Extension October Fruit and Nut Notes newsletter reports, “but grower surveys indicate that lack of best management practices and concerns about expected returns continue to prevent wider adoption of cover cropping practices,”

The article’s authors are UCCE Orchards Advisor Dani Lightle, Amelie Gaudin in the UC-Davis Department of Plant Science, and UC-Davis doctoral student Cynthia Creze.

FIRST IMPRESSIONS

Last winter was the first year of their study, and they plan to plant again this fall, using a soil mix, providing diverse root architecture, and nitrogen-fixation to improve soil health, and a pollinator mix designed to attract bees. Both mixes include radish to address compaction and water infiltration concerns, and white mustard for pollinators.

So far, one thing the researchers have noticed is that rainfall amount plays a big role in determining which of the mix ingredients flourish. For instance, in rows planted to the soil mix in Tehama County, 60 percent of the biomass was white mustard, while in drier Merced County, 59 percent of the biomass was ryegrass. That’s something a grower will need to consider, the researchers advise.

Another thing they are keeping an eye on is whether cover cropping affects frost risk. In Tehama County in February, they noticed that topsoil temperatures were cooler in the cover-cropped treatments than in orchards with resident vegetation, which suggests that the cover crops act as a barrier to heat flow and storage in the soil. However, temperatures at 5 feet during critical frost periods were nearly identical between treatments.

“We plan to directly measure bud temperature in 2019 to better understand whether conditions experienced by the buds are different in cover-cropped or resident vegetation areas,” the scientists say.

PLANTING ENCOURAGED

Planting cover crops has been encouraged by Project Apis m., an organization that funds projects and directs research to improve the health of honey bee populations, while also improving crop production.

Earlier this year, the organization’s Billy Synk hosted on-farm workshops to show growers how planting flowering shrubs and grasses between rows of trees, or on the perimeters of orchards, can help bees and enhance pollination of nuts, according to the Almond Board of California.

Project Apis m. offers a program called Seeds for Bees, which designs and provides seed mixes and methods to establish forage that supports pollinators, according to the organization’s website. The idea is to plant the forage in the fall so it’s blooming by January, in time for the arrival of the almond blossom, the Almond Board says.

The UC is conducting a statewide almond growers survey to gain a better understanding of current barriers and motivators of cover cropping. The researchers say it will bring valuable insight into region-specific needs, as well as operational challenges. Results will be used to develop regional best management practices, as well as guide further research and extension activities, the scientists say.

To read the full newsletter, visit https://bit.ly/2PqmfRx