Healthy ecosystems produce healthy organisms. It’s really that simple.
From gardeners to agriculturalists, it’s becoming increasingly important to understand the role of the soil microbiome in relation to soil health and land rejuvenation. Traditionally, farmers tend to disassociate their target crop from land that it is grown on, focusing on production processes which produce immediate benefits but may be unknowingly detrimental to long-term soil health.
However, recent movements within the agricultural industry are encouraging farmers to look to natural processes as a guideline on creating healthy, sustainable soil ecosystems. These natural ecosystems recycle nutrients and provide natural resistance to drought and disease.
Under this holistic perspective, the target crop is seen as an integral part of a natural system; not just the end goal.
This approach can be unintuitive for conventional farmers who traditionally seek to control soil nutrient levels and biodiversity on monoculture crops.
To understand the benefits of treating the soil like an ecosystem it is vital to first understand what a soil microbiome is supposed to look like.
While the exact composition varies based on land location, healthy soil (i.e. loam) is generally said to consist of 45% rock minerals, 25% air, 25% water & 5% organics. Crucially, it is the 5% organics (e.g. plant roots, dead material, fungi & microbes) which truly drives soil health. Without digging too deep, organic matter adds volume to soil, trapping air and increasing water infiltration and retention.
Figure 1: USDA Soil Composition Diagram
A layer of organic material on the soil’s surface acts like armor for the earth, absorbing water, limiting evaporation and preventing erosion. This organic layer can be plant residue from last year’s harvest, a newly planted cover crop or, in the case of gardens, compost. Aside from protecting the soil, this organic layer will eventually be recycled into nutrients that feed microbial life. As they say, exposed soil is naked, hungry, thirsty and bereft of nutrients.
Central to the health of any ecosystem is biodiversity. A variety of plant species with a variety of root types (e.g. fibrous grass roots, legume, tubers) help to break up hard-packed soil layers while providing food for microbes. The microbes, in return breakdown organic material and recycle soil nutrients. Increasing the volume of plant material promotes microbial development which, in turn, increases the base nutrient levels in the soil, thus increasing plant nutrient availability and uptake.
Of all the life in the soil, one fungus is of particular note. Mycorrhizal fungi colonize plant roots and tap directly into the root system allowing for a nutrient exchange. In this symbiotic relationship, the fungi spores send out thin filaments which form networks surrounding a root. These networks draw in nitrogen and phosphorous from the soil which the fungi then exchange for carbohydrates taken from the plant, thus returning nutrients to the soil. In addition to functioning as a nutrient re-distribution network, mycorrhizal fungi networks also excrete a sticky, glue-like substance which helps build soil structures while boosting water retention.
There are a lot of moving parts in the soil microbiome, but understanding how the elements fit together is crucial to understanding the functional benefits of a healthy soil microbiome. Crucial to a healthy soil ecosystem is a healthy nutrient cycle which depends on several disparate elements working together (i.e. organic material feeds microbiology, which returns nutrients to the soil, which feeds plants, etc,).
By seeking to emulate these natural soil conditions on crop land, the goal is that farmers can reduce crop inputs while maintaining high yields and healthy crops. While, many people argue that nature knows best, and while this may or may not be true, we do know nature costs less.
DeGomez, Tom., Kolb, Peter., Klienman, Sabrina. (2015) Basic Soil Components. Retrieved from http://articles.extension.org/pages/54401/basic-soil-components
United Stated Department of Agriculture. Soil Education. Retrieved from https://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/edu/?cid=nrcs142p2_054330
Bucking, Heike., Kafle, Arjun,. (2015) Role of Arbuscular Mycorrhizal Fungi in the Nitrogen Uptake of Plants: Current Knowledge and Research Gaps. Agronomy, 5, 587-612, dio:10.3390/agronomy5040587. Accessed on May 10/2018