Soil Biology – Dean Moberg

Instructor’s Bio

Dean Moberg is a retired soil conservationist who worked for the United States Department of Agriculture (USDA) for thirty-five years. In that time, he helped farmers, ranchers, foresters, and homeowners in three states on projects ranging from one to over 1,000 acres. As you will learn when you watch the video recording of the presentation he prepared for our soil health cohort, he has also worked on various farms.

As a sophomore biology major at Denver University, Dean became interested in the ecological aspects of agriculture. Professor Stella Coakley helped Dean transfer to the University of California at Davis and convinced her parents, John and Dora Melugin, to invite Dean to live and work on their 23-acre vegetable farm near Modesto, California. John taught Dean to love farming and to respect farmers. Click here to read Dean’s tribute to John upon his death in 2000 (and the story of the cucumbers, the crop duster, and the 12-gauge shotgun).

Dean worked on other farms, too, while earning a B.S. Degree in Plant Science at UC Davis and then a M.A. in Teaching at Cornell University. He milked cows near Willows California, drove tractor in Illinois, baled hay and operated a U-pick strawberry operation in upstate New York. His best farm job (and maybe his best job ever) was making maple syrup in upstate New York. Dean also earned a Ph.D. in Environmental Science and Engineering from Oregon Health & Science University.

After retiring from USDA in March 2020, Dean was elected to the TSWCD Board of Directors in November 2020. Dean and Sara live in the Cedar Mill area and keep a hive of honeybees at a small farm in Washington County.

Learning Overview

Here’s an overview of what you’ll learn. Please scroll down below the bullet points to watch Dean’s presentation.

• In slide 7, Dean describes why farmers should prioritize practices that increase the biodiversity in their soil. As he explains, having a high soil biodiversity encourages “healthy competition”, which reduces the risk of pathogen outbreaks and improves the resistance and resilience of soil ecosystems to disturbance. In Session 2 and 3 of this cohort, you learned how to conduct an In-Field Soil Health Assessment. One of the indicators of soil health included in this assessment is the number of soil organisms present in the soil on your farm. In this section of Dean’s presentation, he reminds farmers that they can build diversity in the soil by increasing the diversity of cover and cash crops, windrows, and hedgerows. This is largely due to the different types of exudates various plants produce and how various exudates feed different types of soil organisms. Timing of when you plant and terminate or harvest your plants are also factors in determining what type of exudates a plant will produce. 
• Slides 10-11 explain why building up stable forms of carbon is critical to your on-farm soil ecosystem functioning properly. During this part of his presentation, Dean gives practical examples of how to build carbon on your farm and how this will support soil biology. 
• In Slide 12, Why the simple practice of keeping a living root in the ground is one of the most impactful and simple practices farmers can do to attract and maintain soil biology. Slide 12 introduces a study conducted in 2019 by Noah Sokol et al. at the Yale School of Forestry, showing that this practice was more effective at building stable organic matter than practices using leaf litter or green mulch.
• Why increasing biological diversity will increase soil function on your farm. Slides 14-18 introduce the concept of the three “functional groups” of soil microbes and the functions they perform for farmers. These slides also describe why soils that contain all three “functional groups” of soil microbes create resilient on-farm ecosystems with high plant productivity. One of the biological groups is ‘biochemical processors’, which are largely soil microbes. These microbes are important to your farm because they regulate 90% of energy flow in soil and are responsible for most of the decomposition of plant organic matter into nutrients that are available for plants. Soil microbes also stimulate plant growth and compete with plant pathogens.
• How to care for your microbes and protect from soil organic matter depletion in tropical climates. Slide 19-20 shares a study showing that microbial activity doubles with temperature and soil moisture. Mineralization rate of carbon is affected by temp and soil moisture due to microbial growth rates, solubility of SOM and movement via soil water, and enzyme activity. But how conditions that are too hot or too wet can slow down mineralization.
• Slides 21-36  Dean introduces the concept of “Hot Spots”, or areas where microbial population size and activity are focused, and why increasing hot spots is a strategy to increase soil biodiversity. Describe practices farmers can use to increase the number of ‘hot spots’.These practices encourage increases in the root zone (“rhizosphere”), litter layer, earthworm and root channels, pores, and aggregate surfaces. As Dean describes in this section, “If you provide the habitat, they will come.” This concept is expressed in a famous quote Dean shares from a 1934 publication by a Dutch microbiologist, Baas Becking: “Everything is everywhere, but the environment selects.” In this section, Dean shares why it is generally not useful to add microbial mixes to soil – as are all probably there already but just need the proper conditions to thrive.” 
• Slides 26-27, Introduces the importance of soil pore space as a key ‘hot spot’ for soil microbes. As Dean explains, when practices destroy pores in the soil, air and water flow are disrupted, organisms are killed and bacteria are unprotected from predation, resulting in a feeding frenzy and rapid but temporary flush of nutrients. A healthy soil tends to have about half of its volume occupied by pores. Since soil minerals average around 2.65 g/cm3, a healthy soil with 50% pore space has a bulk density of about 1.33 g/cm3 or maybe even less. Compacted soils have <50% pore space and thus higher bulk densities. As part of this cohort, you will be receiving test results from the bulk density soil sample we submitted to UH Crow Lab. If your bulk density is high, you’ll want to focus on practices that reduce compaction, increase soil aggregate structure and provide habitat for soil biology.
• In slides 28-30, Dean reminds farmers that if they want to improve the soil structure on their farm, they should grow cover or cash crops that have mycorrhizae, add organic matter, and find creative strategies to keep a living root in the ground and increase poor space. As he explains, aggregates are created by soil organisms using physical and chemical processes. Glomalin is a glue-like substance that causes aggregation of soil particles, increasing pore space, adding structure to your soil and reducing soil compaction. Glomalin is a glycoprotein produced by hyphae of arbuscular mycorrhizae. We all love Brassicas, but they don’t have mycorrhizae. However, most other crops typically grown by farmers do have mycorrhizae. Soil aggregates are also physically created from fungal and bacterial filaments, earthworm castings, and plant roots.