In California’s central valley, there is a violent battle taking place between nature and machine. On one end of the arena is the Iron Wolf, an aptly named metal monster weighing in at 100,000 pounds. On the other end stands an orchard, the roots of its trees holding onto the ground for dear life. When the Iron Wolf is finished, it will look like an orchard was never even there. The trees will have been uprooted by the wolf’s claws and ground to shards by its teeth. Finally, the remains of the trees will be incorporated into the earth from whence they came.

iron wolf in almond orchard

An old orchard falling to the teeth of the Iron Wolf in the name of Whole Orchard Recycling. (Photo Courtesy of almonds.com)

This was how a study began in 2008 at the University of California Kearney Agriculture Research Extension Center in Parlier, CA, where researchers aimed to test the long-term effects of a management strategy called Whole Orchard Recycling (WOR). As the previous scene depicted, WOR involves grinding up old orchards and depositing the biomass back into the soil. California’s central valley is responsible for producing 80% of the world’s almonds. Almonds are also perennial crops that seem to be sensitive to the effects of climate change. In order to protect this lucrative industry, research is needed to determine the long-term effects of techniques like WOR in terms of crop resilience and climate change mitigation. The study was set up to compare two treatments – WOR and a burn treatment in which old orchards were uprooted, burned, and then incorporated into the soil as ashes.  After these two soil treatments were completed, a new almond orchard was planted.

Soil samples were collected from these two treatments 9 years later to analyze chemical, physical, and hydraulic properties of the soil, as well as microbial activity, overall soil health, yield, and productivity. In addition to measuring all of these factors, researchers decided to also test how the two treatments would affect the resilience of the trees in the event of insufficient water resources. To do this, two irrigation treatments were added – one that gave the trees a sufficient amount of water and one that irrigated at only 80% evapotranspiration, that is more water was leaving the system than coming in. The researchers had hypothesized that WOR would add large amounts of biomass with a lot of carbon, helping carbon sequestration, soil health, yields, and productivity.

What they found was that WOR out-performed the burn treatment in many aspects. Grinding up such a large amount of biomass and adding it back into the soil resulted in the trees in the WOR treatment producing more almonds than those in the burn treatment. The soil of the WOR treatment also contained more soil organic matter, more soil organic carbon, and more enzyme activity. The soil was also more stable while being less compacted. It was able to retain more water and allow water to infiltrate more quickly. In terms of irrigation, researchers found that the trees in the WOR treatment suffered less under insufficient irrigation conditions than the burn treatment, with more water being held in the soil and the trees themselves.

But why do all of these performance parameters matter? Well, soil organic matter can add a lot of nutrients to the soil, making it more hospitable for crops. The fact that WOR resulted in more soil organic carbon means that it could be an important tool for farmers to sequester carbon in their soils and mitigate the effects of climate change. Soil aggregate stability means the land will potentially hold up better to stress and erosion. Water retention and infiltration is especially valuable in this region of California, which tends be dry and prone to droughts. These findings can certainly go a long way in terms of helping farmers improve their soil and the resilience of their crops while making a positive impact on the fight against climate change.

Study:

Jahanzad E, Holtz BA, Zuber CA, Doll D, Brewer KM, Hogan S, et al. (2020) Orchard recycling improves climate change adaptation and mitigation potential of almond production systems. PLoS ONE 15(3): e0229588. https://doi.org/10.1371/journal.pone.0229588