In orchards, cover crops help build soil health, suppress weeds, control erosion, and—of particular interest to growers in drought-prone areas—increase water-holding capacity. It may seem counterintuitive that adding crops could ultimately help reduce irrigation needs, but done correctly, this can be the case.

Why consider cover crops in orchards

Research has shown that cover crops add organic matter and nitrogen back into the soil, increasing the nutrients available to the cash crop. They can reduce dust, attract beneficial insects, and convert mineralized nitrogen in the soil to more stable organic forms, which limits leaching.

Cover crops enhance water infiltration of the soil by stabilizing soil aggregates and creating root channels. This can help mitigate runoff of irrigation and rainwater, increasing the stored soil moisture available to the cash crop.

Of course, the cover crop itself will need water—but drought-tolerant selections, such as summer-dormant native perennial grasses, will need very little. In fall and winter, when more moisture is available, clovers and legumes provide excellent ground cover while also depositing available nitrogen for the cash crop.

Choosing the right cover crop mix

Choosing a cover crop can be difficult because of the wide range of seed mix options available. It’s helpful to begin the process with a specific goal in mind: Do you need to add nitrogen to the soil? Address salinity issues? Or is the top objective to increase water-holding capacity?

Testing cover crops in a few areas of the orchard is one way to evaluate the fit without making a huge investment. Alternatively, growers can look to an advisor with knowledge of what works well in local conditions.

green manure cover crop

Cary Crum is a regenerative ag specialist at California Ag Solutions. He generally recommends a mix that combines deep-rooted and ground-cover species—but notes there’s no one-size-fits-all prescription. “Every situation is unique, so it’s our job to put together a custom mix that will fit your orchard’s needs,” he says. For Crum, that starts by asking questions such as:

  • When will you plant the cover crop?
  • How will you germinate the crop?
  • How will you manage it during growth?
  • When and how will you terminate the cover crop?
  • How will you make the above-ground biomass dissipate prior to harvest?
  • How will you adjust your fertility program to make up for nutrient tie-up caused by additional soil organic matter?

Crum is seeing impressive results when cover crop selection is done right. “We are finding that we see virtually net-zero water use in trees with the proper mix of cover crop plants, because of all the biological benefits of the plant roots, increase in water filtration, and species diversification provided in the orchard. The bee population has been more healthy, and insect pest control has also been better.”

When to plant and terminate cover crops

Planting a winter crop takes place after the cash crop harvest. (Note that it may be necessary to work around other management needs in the orchard at this time of year, such as pruning and chipping.) In general, growers aim to keep the cover crop going as long as possible before terminating it in the spring.

For perennial grasses and legume sods, it’s important to mow as soon as possible in February or March when the soil surface is dry enough to be driven over with machinery without causing compaction. Mowing at this time will reduce weed competition and prevent shading of small clovers and grasses that should still continue building ground cover.

almond orchard with cover crop

Another popular type of mix is “green manure” cover crops. This mix should not be terminated until it has maximized biomass production, typically closer to late April or early May. Disking or rotary mowing will help to incorporate the residue into the orchard floor.

In very dry conditions, it may be necessary to terminate the cover crop early to save water for the trees. Even when this is the case, the ground cover residue will still provide organic matter and help with erosion control and water holding capacity.

For more information on using cover crops in orchards, refer to the Cover Crop Best Management Practices Guide, a collaboration between the California Almond Board and University of California. This useful reference provides a detailed calendar for planning seed purchases, planting options, in-season mowing, and termination of the cover crop.

Orchards Sustainability

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