Digging Into Soil Health
If you take an example of potato or mustard production, farmers prepare a seedbed of fine soil particles using multiple (intensive) tillage operations. Many farmers believe that it allows an easy flow of air and water, a warmer, and competition-free environment suited to seed germination. However, the fine particles and small pores characteristic of tilled soil are ultimately unstable, leaving fields vulnerable to erosion and compaction over time. This is because tillage can destroy natural soil structure, weakens soil aggregates and impedes plant root growth.
Soil aggregates are groups of soil particles that bind to each other more strongly by clay particles and organic matters. Soil aggregates are the basic unit of soil structure, which is often known as the physical fertility of the soil. Following intensive tillage operations can increase top-soil erosion and accelerate nutrients depletion. Intensive tillage can be a harmful practice from a soil health perspective as well. Then a question arises: what is soil health?
Soil health is a highly pronounced buzzword in agricultural and environmental sectors over the last decade, but the earliest references on it date to over 100 years ago. Some say that soil health is a new way of pronouncing soil quality. While awareness of soil health is increasing, it is important to have a good understanding — why do we care, how it is measured, and how to manage it for optimal and sustainable delivery of the ecosystem services that soil provides. Before jumping into soil health, let’s dig into soil quality first.
Soil quality is a more specific term that refers to the ability of the soil to perform a particular function or set of functions. For example, it may be assessed in terms of its ability to support crop production and/or to provide habitat for soil organisms. Once you define the specific functional attributes, it can be measured by various indicators. An example is that we can determine soil quality by measuring soil organic matter and soil nutrients status for crop production.
While it is true that soil testing services the purpose of monitoring soil, testing focuses mainly on the ability of the soil to provide plant nutrients, but it does not serve the measuring of overall soil quality. Neither can it be determined by measuring only crop yield, water quality, or any other single outcome.
Soil quality is very different from air or water quality, which is not limited to the degree of soil pollution but more commonly defined by the interactions of a particular soil’s measurable physical, chemical, and microbiological properties. These properties can be managed and adjusted by farmers in the context of the inherent capability of a particular soil. Soil quality is the historic origin of the soil health term.
When we portray soils as dynamic and complex living systems, soil health refers to the capacity of soil to function as a vital living system to sustain biological productivity, promote environmental quality and maintain plant and animal health.
The biological components of soil, including bacteria, actinomycetes, fungi, algae, protozoa, nematodes, mites, insects, earthworms and larger soil-dwelling animals, as well as plant roots and underground plant parts, all interact in what is collectively referred to as the soil food web and are all critical components for soil health. Biological components of soil affect soil structure, erosion and water availability. Similarly, they are crucial to decomposition, nutrient cycling, breakdown of toxins, and suppression of pests, and are responsible for a large proportion of the world's genetic diversity. Soil health is synonymous with sustainability in a broader view.
According to the Merriam-Webster dictionary, "health" is the "condition of being sound in body, mind, or spirit." We can restructure this definition of health to apply to the soil as "the state of the soil being in sound physical, chemical, and biological condition, having the capability to sustain the growth and development of land plants." Again, multiple definitions of soil health exist, it is easy to understand and support soil health, however, it has been difficult to capture its definition with measurements. The challenge is that farmers, researchers, homeowners and conservationists could all view soil health differently because soil function means different things to them.
For a farmer, the primary function of the soil is to hold enough water, sustain enough nutrients and provide insect-pest control environment to produce sustainable crops. For a general homeowner, the primary function of soil is to provide nutrients for their lawn and garden. So, it depends on who you are and what you expect the soil to do for you. Overall, soil health represents those four principles to manage soil in a way that improves soil function: maximize presence of living roots, minimize field disturbance, maximize soil cover and maximize biodiversity.
Soil Health Measurement
When you visit a medical doctor, you will be subjected to many different key measurements, such as temperature, blood pressure, pulse rate, etc., that are used as indicators to get a sense of a person's overall health. In a similar way, there are numerous indicators to measure soil health that are sensitive to changes in soil processes and represent connections among soil biological, chemical and physical properties.
Just as vital signs help to provide a status of human health, soil health indicators are being developed to help us tell healthy soil from unhealthy one. A sandy soil and a clay soil can both be healthy, but they obviously have quite different water and nutrient regimes and use potentials. Yet, there is not a widely accepted, standardized way to measure soil health and these indicators do not always provide consistent results. However, scientists globally are putting their efforts into understanding and improving the measurement of soil health. Critical theories like Soil Health Gap, which defines, grassland or prairies which have not been cultivated, can be used as a benchmark to measure the potential capacity of your land.
Soil Health Scorecard
There are many versions of soil health scorecards, which bring collective information about the biological, chemical and physical properties of soil. For example, a widely popular Cornell University’s Comprehensive Assessment of Soil Health (CASH) method measures soil health by defining a set of indicators and a procedure resulting in a number between 1 and 100, ranging from highly unhealthy to shiningly healthy. But it is important to note that soil health assessment report provides the relative score and does not translate to a direct prescription for soil management like a fertilizer recommendation, one you would get from a conventional soil fertility testing service.
You can perform a quick assessment of soil health in your field by digging up a shovelful of cultivated soil and counting the number of earthworms. If there are 10 earthworms that is a good number for soil health scoring. Similarly, you can compare your cultivated soil with undisturbed soil and observe, for example, how deep roots go, does soil clod break apart easily? You can also compare soil color; the darker the color indicates more soil organic matter or organic carbon. In other words, it gives an indication of soil health.
Healthy soil produces healthy foods, a way to keep healthy people. It is a universal fact that doctors take care of us when we are sick, but the farmers are the ones who can keep us healthier. Let’s give the technical and financial assistance to farmers to make the transition to the farming practices that prioritize soil health.
Dr. Panday is a soil scientist specializing in carbon and nitrogen cycling in agroecosystems.