Challenges: Perspectives of Expert Growers

Cover Cropping in Nut Orchards: Residue, Soil Cracking, and Mechanical Harvest

While perennial orchard systems seem in many ways ideal for integrating cover cropping practices to improve soil health, increase pollinator habitat, and provide water infiltration & retention, among other benefits (Wood & Bowman, 2021; Crézé & Horwarth 2021), concerns about cover crop residue in mechanical harvesting systems abound. For example, one of the most significant concerns expressed in a statewide survey of almond growers is debris interfering with nut harvest (Gaudin et al., 2020).

However, growers who are experienced with cover crops in their orchards overwhelmingly find that cover crop residue did not interfere with harvest. To the contrary, some find cover crops to be especially beneficial, such as when cover crops reduced or filled soil cracks, thereby reducing nut losses. Additionally, some growers found cover crop residue diminished dirt brought in with the harvest. With pecans, which are harvested late in the fall, maintaining vegetation through harvest helps allow equipment access, even if it rains. 

Kelsey Creek Orchards

David Mostin of Kelsey Creek Orchards organically farms 15 acres of walnuts and 15 acres of pears. He has planted cover crops since he acquired the walnuts in 1986 and has added cover cropping into his pear orchard a few years ago. After experimenting with different management practices over the years, he finds it much easier now with a seed drill instead of the broadcast seeding he used to do. The seed mixture currently used is a Biobuilder mix: 40% cayuse oats, 30% bell beans, 20% biomaster peas, and 10% common vetch seeded at 100lb/acre. The cover crop is rotary mowed high in the spring and terminated with a flail mower two months later. The flail mow is repeated close to the ground pre-harvest. Cover crop residue has never presented a problem for David Mostin. He says, "the harvest is so late compared to when everything has been [mowed]...during the year, it's never been a problem."

Detailed information about Kelsey Creek Vineyard's cover cropping practices.

Bullseye Farm

Nick Edsall is the orchard manager at Bullseye Farm in Yolo County, where he oversees 6,000 acres of walnut, pistachio and almonds.  Between the different orchards, Nick says “it's a lot easier for us to cover crop in walnuts and pistachios because we don't have the nuts on the ground in the pistachios, and the walnuts we harvest off the ground, but they're really big and they're round and they roll easily. So you don't have as much problem with residue on the ground, for sure”. He finds that by the late walnut harvest, most residue is already broken down.  In an orchard with very heavy clay soils, the ground had such large cracks that “we were losing nuts in the middle when we swept them up…we banded compost in the middle where the cracks were and planted triticale.” Triticale was chosen for its strong and fibrous root system; it turned out to be “a huge success” said Nick Edsall. Another benefit they found of having cover crops in orchards with rough ground or very loose soil is that “you can actually get that stuff to come in with just the residue. And then you're not bringing dirt in. And the residue is really easy for the machine to clean out, but not this dirt.”

Detailed information about Bullseye Farm's cover cropping practices.

Erdman Family Farms

Kim Gallagher is a fifth-generation farmer growing 380 acres of almonds south of Arbuckle in Colusa County. They have used cover crops throughout their entire orchards for the last two years. They initially just planted small areas and every other row until they realized there were proven benefits. "The science is out. [Cover cropping] is actually something we should be doing. And so we just bit the bullet, and now we cover crop everything." When they first started, they did have some concern. "Were we going to be able to make it through harvest having a clean product or were we going to…have just a bunch of stuff in there?" The outcome, she says, "was awesome." In the beginning, cover crops were broadcast seeded after discing; then, they used branches to cover up the seeds. Recently they bought a drill planter. Partnerships with Xerces Society, NRCS, CAFF, and Project Apis m. have helped deepen their knowledge, inform seed choices, and provide cost-sharing opportunities. The orchards are on a drip-tape irrigation system, which means the cover crop residue is "pretty much gone by August when we start harvest, if we mow it in May." Using a de-sticker during harvest ensures they have no issues with residue. This was a relief since "the main reason we didn't want to do cover cropping was because of residue at harvest and [that] has not been an issue here."

Detailed information about Erdman Family Farm's cover cropping practices:

• Erdman Farms: Bearing almonds
• Erdman Farms: Non-bearing almonds
• Erdman Farms: Walnuts

Pacific Gold Agriculture

The owner of Pacific Gold Agriculture, with almond and pecan orchards in Colusa County, Ben King, at first only cover-cropped half of his 350 acres of almonds but has now expanded to cover crop his entire orchard. They have found cover crops beneficial in their operation on multiple fronts: supporting pollinators, increasing soil health and soil organic matter, increasing the water holding capacity, and even improving harvest conditions by reducing the number of large cracks in the soil into which almonds disappear. Cover crop seeds used in the almond orchard are from the Project Apis m. soil builder mix: 30% Triticale, 35% Bell beans, 28% Peas, 2% Canola, 2% Common yellow mustard, 3% Daikon Radish. King keeps the tree rows free of cover crops, noting that he needs to keep them clear to maintain drip lines. The vegetation grows tall and can obstruct the view required to notice problems in the drip lines. It would also be challenging to rake around the tree to collect nuts if vegetation were in the way. Additionally, he has concerns it would provide cover for rabbits and rodents to chew drip lines. They have found their operation needs to be proactive at managing the irrigation with cover cropping. However, cover crop residue in the strip gets fully broken down before harvest and has never been a problem. Cover cropping in the pecan orchards is especially important. Notes King, "With pecans, you need to have turf or natural vegetation to have firm ground to facilitate entry into the field even if it rains around harvest time, which occurs October to December…Due to full coverage sprinklers, everything on the orchard floor is getting wet. So if you don't plant a cover crop, you will have weeds almost year-round." Last year the farm started to work with the Environmental Defense Fund to plant a monarch butterfly habitat mix instead of resident vegetation in the pecans.

Detailed information about Pacific Gold Agriculture's cover cropping practices:

• Pacific Gold Agriculture: Almonds
• Pacific Gold Agriculture: Pecans

Spotlight on: Soil cracking

Growers have found that cover crops and their residues ameliorate soil cracking. Soil cracks expand the soil-air interface, potentially increasing evaporation from soil (Ritchie & Adams, 1974). The frequency, size, and rate of soil crack formation can influence not only water in soil, but also air and heat movement, all of which can impact crop productivity (Somasundaram et al., 2018). Nick Edsall from Bullseye Farm in Yolo County commented that the cracks in the soil were so extensive "we were actually losing nuts in the soil, in the middles when we'd sweep the [almond] nuts. Back then, the price was somewhere around $3 a pound. So you could actually count your losses." Similarly, almond grower Ben King has observed that cover cropping has helped reduce cracks into which nuts would disappear.

Spotlight on: Brassica dominant cover crops

Brassica cover crops are popular components in mixes designed to support pollinators, and some growers observe that they produce less organic matter than many other cover crop species, which can lead to a quick decomposition. However, they must be terminated before they get tall and woody. Ben King has found that this could happen as early as May, so he mows right after the mustard blooms. Nick Edsall has found that mixing brassicas into multi-species mixes can keep them from getting too tall. “When you plant a multi-species mix…they all keep each other in line. So we'd have a three foot tall cover crop where, if we'd just planted mustard, it might get six feet tall and kind of get out of control,” explained Nick.