By Dennis Pollock, Ag Alert
Several people who are knowledgeable about cover crops gathered virtually for a webinar presentation on cover crops in orchard systems, presented by the Madera/Chowchilla Resource Conservation District.
That was followed the next day by visits to almond orchards showcasing cover crops in Madera and Chowchilla.
The webinar’s lead-off presenter, Jeff Mitchell, with the University of California, Davis, Department of Plant Sciences, is no stranger to the topic of cover cropping. For more than two decades, he has been pioneering use of covers and no or low tillage in field crops at the UC Westside Research and Extension Center in Five Points.
He opened by describing market demands for farmers to pursue regenerative agriculture. And he cited significant growth in tons of organic matter and carbon as a result of cover crop use in Five Points.
Mitchell, as he has in previous presentations, showed the differences in how water infiltrates soil with a cover crop, whereas it runs off places where there is no cover crop. That principle applies to both field crops and orchards, he said.
Vivian Wauters, a postdoctoral researcher at UC Davis, discussed research updates on cover crops in almond orchards.
She said cover crops do not necessarily interfere with the need for clean alleyways at harvest, “if well managed.” In addition, she said, there will be new opportunities to skirt the clean-alleyways issue with off-ground harvests that are being discussed.
Wauters said legumes decompose faster, and that cover crops can be terminated after bloom by mowing or using an herbicide.
She also said research has shown no negative impacts on yields and trends toward yield increase in very compacted orchards, an increase of as much as 225 pounds per acre in the second year of cover cropping.
Wauters showed pictures that illustrated differences in the capture and conservation of winter rainfall in cover-cropped orchards in Merced.
Cover crops were also found to result in a decrease in the amount of sodium contained in irrigation water.
“Cover crops can be managed for pollinator resources without negatively affecting bee pollination services in almonds,” Wauters said, noting that it has been learned that flowers in orchard-adjacent wildflower plantings do not compete with almonds for bees. Diverse diets and longer sources of forage result in healthier bees, she said.
Wauters said cover crops may pose less frost risk than conventionally thought, adding that varieties tested for cool-season cover in California include the Austrian winter pea, balansa clover, black oat, cereal rye, crimson clover, daikon radish and hairy vetch.
Margaret Smither-Kopperl, manager of the Madera/Chowchilla Resource Conservation District, talked of cover crop selections and management in the Central Valley.
She described site preparation and use of a no-till drill and tillage aimed at creating a firm seed bed. Next comes drilling or broadcasting seed. She called good soil-to-seed contact essential for success.
Smither-Kopperl said other considerations include whether the cover crop will be entirely rainfed or if an irrigation system will be used.
“Drip or microsprinklers in orchards can lead to two environments: growth under the trees, desert in the rows,” she said.
Cool-season cover crops can be planted in the fall or early spring, Smither-Kopperl said, and will tolerate cold temperatures and some temperatures below freezing. Warm temperatures will cause plants to mature, set seed and die. There are varying degrees of drought tolerance, depending on species and cultivar.
Warm-season cover crops are planted in spring, after danger of frost has passed, and may be planted through the summer to early fall, she said. Freezing temperatures will kill these crops. They tolerate high summer temperatures and have varying degrees of drought tolerance, again depending on species and cultivar.
Smither-Kopperl said cereals and grasses have vigorous root systems, are good for soil building, reduce erosion, increase water infiltration and holding capacity, concentrate nitrogen and phosphorus, increase nutrient cycling and suppress weeds and diseases.
Legumes are good for nitrogen fixation, nutrient cycling, developing a main taproot and improving water infiltration, she said, noting that some species support pollinators and beneficial insects, and aid in pest and weed suppression.
Brassica and radish provide strong taproots, reduce soil compaction, scavenge nitrogen, increase infiltration and water holding capacity, Smither-Kopperl said. Some of these species also host pollinators and beneficial insects, and can help in pest and weed suppression.
She said it is important to keep in mind variability in seed size and to choose equipment that is compatible for planting. Seed size determines optimum planting depth; seed planting depth is commonly twice the diameter of the seed.
Cary Crum, a crop consultant with California Ag Solutions Inc. in Madera, said it’s best to eliminate glyphosate from a production system using cover crops, and to treat the cover crop with the same attention paid to a primary crop.
Crum advised farmers to take care in timing mowing and mowing frequency, and to have a termination plan.
He said planting can be done by broadcasting seed, using a conventional or no-till drill and applying by air. Planting too early in the fall may mean a lack of rain results in poor germination, he said, or that seeds germinate but die for lack of moisture.
The webinar is available on YouTube by searching for its title: Cover Crops in Orchard Systems Workshop.
