Soil Health Principles
Sections in this Guide:
Regenerative agriculture does not have any uniform definition or set of rules, but the major core philosophy shared across successful regenerative farmers is to promote soil health. Improving soil health in turn supports crop productivity, ecosystem services, and farm operational resilience. A vast majority of cash crops grown across the world, from grains and cereals to vegetables and perennial fruits, cannot be produced on a large scale without relying on soil. In fact, over 95% of food produced globally is cultivated in soil. It is therefore reasonable to conclude that soil is the most valuable resource for a majority of farming operations, and is the basis for regenerative agriculture management.
The term "health" is generally only applied to living organisms, and this is why the phrase "soil health" was coined in reference to the many living organisms that inhabit the soil environment. This includes microorganisms like bacteria and fungi, nematodes, earthworms, and many others. While conventional agronomic theory often considers the physical properties of soil (texture, density, water holding capacity) and chemical properties of soil (nutrients, pH, CEC) to be the primary drivers of crop productivity and main focus of management, biological properties (nutrient cycling, crop residue decomposition, biocontrol) are becoming an increasingly heavy focus of farming as regenerative agriculture gains wider adoption and the benefits of soil biology on crop productivity become more widely known.
Intro to Soil Health and the Three Components of Soil
It is very important to note that soil health is not defined solely by biology and does not replace the value of understanding and managing soil physical and chemical properties. On the contrary, the chemical and physical components of soil interact with biology, and soil biology in turn interacts with soil chemistry and physical properties. Soil health therefore encompasses all three of these primary components of soil, as well as their associated interactions and overlaps with each other. The Venn Diagram to the right provides some examples of these interactions between the three components of soil, including the ability of soil microorganisms to unlock nutrients by performing solubilization (a biochemical process) or alleviate soil compaction by creating small microscopic tunnels in the process of bioturbation (a biophysical process). Natural biological, physical, and/or chemical processes like these support crop productivity and when promoted effectively can reduce reliance on external inputs like fertilizers, fungicides, and fuel for deep tillage. The six principles listed below offer a framework for promoting soil health to regenerate agricultural soils and optimize the soil's chemical, physical, and biological properties. Most regenerative farmers have developed management programs that adhere to all of these six soil health principles in some capacity.
The Three Interrelated Components of Soil:
Biological, Physical, and Chemical Properties
Six Principles of Soil Health
Consider Context
The specific context of each farm operation heavily influences what tools and management decisions will and won't work. Contextual factors include soil type, rainfall, available agricultural input portfolios, social values, economic conditions, and many other aspects of a farm. The specific cover crop mix or soil amendment that works effectively on one farm may not work on another farm just a few counties away due to differences in context. Immediate no-till transition may work well in one soil type but require an initial deep tillage event in another soil type to break up a hard pan compaction layer. Considering context is arguably the most important soil health concept because it helps narrow down what the other soil health principles should look like in real-world practice.
Minimize Soil Disturbance
Documented benefits of reducing soil disturbance include increased nutrient cycling and water holding capacity, along with reduced soil erosion and fuel costs. Tillage can serve as an important agricultural tool to control weeds or prepare seed beds. However, excessive tillage causes erosion and can harm beneficial soil biology. The increased adoption of no-till farming in the 20th Century occurred largely due to the agronomic and environmental benefits of reducing soil disturbance. Tools like strip tillage, vertical tillage, or other minimum tillage techniques serve as viable options to reduce soil disturbance where no-till farming is a challenge. Minimizing chemical applications to soil in the form of crop protection products and synthetic fertilizers is also an important way to reduce disturbance.
Maintain Living Root Systems
Crop root systems stabilize soil while providing habitat and sugars to soil microbes in exchange for benefits like protection and nutrients. These beneficial microbes thrive and grow in the soil when plant roots are present to offer habitat and food. Fallow periods reduce the populations of these microbes as they lay less active without roots to inhabit or sugars from crop roots to feed on. This reduces recolonization of future crop roots. Maximizing time periods with crop roots in the ground enhances the symbiotic relationship between microbes and plants. This contrasts with the common belief that crops are strictly extractors of resources from the soil. It is now widely known that crops can also contribute to soil health by "feeding" carbon-rich sugars to soil microbes through their roots and by returning nutrients to the soil as crop residue decomposes.
Increase Biodiversity
Biodiversity includes any living organisms, from cash crops and cover crops to livestock, insects, and soil microbes. The benefits of expanding biodiversity on a farm are similar in theory to the benefits of diversifying investments. A diverse portfolio offers stability and minimizes risk because it places investment across a range of assets that will likely be impacted differently by unstable market conditions. Put concisely, diverse portfolios offer financial resilience. Similarly, diversified cash and cover crops offer farm resilience by reducing disease carryover, pest pressure, risk of soil nutrient imbalances, and market volatility risks. Beyond crops, promoting diverse populations of soil microbes, insects, and livestock also offer benefits to farm resilience and productivity.
Feed Soil Microbes
Soilborne microorganisms perform critical natural processes to support crop productivity that are not heavily recognized in conventional agronomy, but are becoming increasingly well documented. Microscopic creatures such as bacteria and fungi supply plants with nutrients, build organic matter, promote plant stress tolerance, and suppress pathogens. These biological benefits of soil microbes can be maximized by stimulating or "feeding" them. Healthy crops feed soil microbes by releasing sugary compounds through their roots called root exudates, and crop residues feed microbes as they decompose in the soil environment. Application of biostimulants such as humic acid, plant extracts, manure, and compost teas also feeds soil microbes to enhance their benefits on crop production.
Keep Soil Covered
Covering soil with crop residue or mulch helps "armor" the soil by serving as a physical barrier to erosion, reducing weed establishment, holding soil moisture, buffering stressful temperature swings, and offering crop residue as a food source to soil microbes which release plant nutrients in the process of decomposition. In large scale row crop farming, mowing or rolling cover crops to kill and deposit their residue on the soil's surface is the most common and economically effective way to maintain cover. In specialty crop operations, plastic mulch is commonly used to maintain soil coverage. While plastic mulch can effectively retain moisture, it can also leach plastic compounds into the soil and it does not offer the benefits of feeding microbiology and releasing nutrients like organic mulches or crop residues.
Examples of agricultural practices that fulfill soil health principles
Consider Context
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Ask neighbors, regional partners, and other farmers what soil health practices have worked effectively for them and what hasn't worked
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Select cover crop varieties based on regionally adapted traits like termination dates, moisture needs, and resistance to relevant environmental stressors and pests
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Adjust cash crop rotations based on limiting environmental factors (i.e. consider silage sorghum instead of silage corn in highly drought stressed regions)
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Use soil tests that are considered reliable in specific soil types of focus
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Take into account plant phenological stage in tissue sampling and fertility management
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Explore local alternative market options, such as local businesses, restaurants, livestock operations, or produce outlets
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Consider both the similarities and differences between your operation and others when applying their findings of colleagues in your own agronomic practice
Agricultural practices that support multiple soil health principles:
This table contains a handful of examples of agricultural practices that fall within the scope of specific regenerative ag principles.
Considering context is an important aspect of any management practice decision because context helps determine the specific operational details (cover crop variety selection, livestock species, available biostimulant products, etc) that are necessary to ensure that practice adoption is feasible and successful.
You may notice that many practices overlap and fulfill multiple principles. Cover crops offer the potential to fulfill all six soil health principles.
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What does every agricultural practice that fulfills at least one soil health principles have in common?
They all support natural soil biological processes that contribute to crop health, resilience, and yield
Additional Resources on Soil Health
