Visit the typical almond farm in California and you’ll see rows of trees stretching to the horizon, forming an arching canopy over a corridor of dry, bare dirt. A harvester with a giant mechanical arm moves from tree to tree, vigorously shaking each trunk, forcing the nuts to drop to the dirt below, like confetti on a New Year’s Eve celebration. The farmers then rake and dry them on the bare orchard floor.
But those bare floors aren’t natural, and some farmers have decided that clearing vegetation around the trees to create them is a mistake.
While it makes collecting the almonds more difficult, planting cover crops between the trees can improve soil health. Many farming practices lead to soil degradation, which was responsible for the fall of civilizations that could not agronomically support their populations: archaeologists have associated processes like soil erosion with the rise and fall of civilizations in the Middle East, Greece, Rome and Mesoamerica, for example. So, promoting soil health is critical to maintain the soil—one of our most precious resources. Cover crops support an abundance of soil microbes that nourish plants and promote sustainable, productive agricultural lands.
Tom and Dan Rogers are heeding that advice. They maintain almond orchards on farmland that has been run by their family for over 100 years, and for decades the brothers followed the maxim a “clean floor is the best.” Tom recalls feeling a sense of pride looking across the clean, well-maintained ground between his trees. Not only does bare soil make harvesting easier, but allowing cover crops to grow means higher water demand and extra effort (they have to be mowed to get to the nuts). Using them can make a farmer stand out among his or her neighbors and seem a bit odd.
But several years ago, the Rogers brothers began learning about research on the benefits of cover crops for soil health. Tom Rogers defined health for his orchard the same way he defines human health: “To be healthy is to have strength, vigor, and resilience.” He notes that malnourished people lose these qualities, and so will his trees. So, the brothers are now starting to incorporate a variety of cover crop plants into their orchards. Though establishment has not been easy, owing to the lingering effects of herbicides, they are committed to using cover crops to nourish their soils and trees.
The use of cover crops was more common in the U.S. before herbicides became readily available and favored for weed control. In addition to chemically intensive management, recently more attention has been brought to the toll that maintaining bare soil takes on the soil biology. Without carbon inputs from plants, the abundance and diversity of soil microbes begin to plummet. Similar to how microbes in our gut help us to metabolize food, research has revealed that microbes in and around plant roots have a suite of traits that benefit plant growth and productivity.
Many of the microbes in the soil have evolved alongside plants for millennia. In exchange for fresh carbon, microbes scavenge the soil to bear plant-available nutrients like nitrogen, phosphorus and iron. Plants and soil microbes are so entwined that some microbes themselves become living extensions of the plant root system. Others produce plant growth hormones and alleviate plant stress responses to conditions that would typically stunt plant growth.
Numerous studies indicated that the absence of plants can negatively impact the abundance and diversity of microbes in soils. When microbial populations drop in number, there are fewer beneficial microbes functioning and less ability to competitively displace pathogens. Many microbial species thrive best under specific environmental conditions, which change a lot in a growing season. So, when biodiversity declines, there are fewer species, thus beneficial microbial functions occur under more limited circumstances.
This is where cover crops come in (which aren’t necessarily “crops” in the sense of plants that are harvested for food or other uses). They can promote healthy and diverse soil microbial communities by inputting a “microbial lunch” into soils, a full menu of compounds exuded from roots and decaying roots and leaves. Plants shade the soil, preventing it from becoming baked and dry. Plant-covered soils typically have improved abilities to retain nutrients and filter and store water, so they reduce fertilizer and pesticide leaching and are more eco-friendly.
The Rogers brothers foresee these benefits outweighing some of the challenges in managing their orchards with cover crops. For example, they will need to select cover crop mixtures that do not compete with their trees for water, time the planting just right—and prior to harvest, they’ll have an additional task of mowing down the cover crops so they can collect their almonds.
Their biggest concern is that if rainfall occurs on/around their harvest, the ground under the mown-down cover crop will stay wet longer and the almonds shaken off the tree could rot. The financial risks and management headaches associated with cover crops are wide-ranging and are cause for low adoption rates in many cropping systems.
The Rogers brothers anticipate that some years may be tougher with their new strategy, but that their healthier orchards will be more resilient and produce almonds with higher nutrient and oil contents. The brothers believe that they can modernize older, sustainable practices, like cover crops, keep their orchard productivity high and provide a more nourishing product to their customers.
They are not alone in the movement to promote soil health using cover. Cover crops were a central concept in David Montgomery’s book Growing a Revolution: Bringing Our Soil Back to Life, and they are popular in many regions of the U.S. Cover crops are also championed by the Soil Health Institute, a nonprofit organization aiming to converge science, farmers, and policy makers striving to revitalize degraded soils. The U.S. Department of Agriculture and the California Department of Food and Agriculture are supporting research, demonstrations and education about cover crops through soil health and agricultural sustainability initiatives. Recently, grower surveys indicate that farmers rank soil health as a top priority.
But cover crops in the Western U.S. are still only used on a very small percentage of farms. Perhaps this is where the general public comes in. If people value food grown with soil health practices, then produce buyers, like commercial grocery store chains, will push for it. Unfortunately, without that push, soil health practices may remain limited to a few "oddball" farmers who really envision the investment.
The future of the Rogers brothers’ orchards looks much greener. A lush assortment of cover crops between their trees will brighten the drab, dirt corridors that used to line their farms. The quiet stillness of the dirt will be replaced with buzzing activity of bees and beneficial insects. Come fall, the harvester will confetti their ground with almonds. Only this time the ground on which those almonds lie will be rich, fertile and alive.