What Is Fertility? – Soil Health

(Eighth in a series)

Not that long ago, the phrase “soil health” would likely have been regarded as nonsensical—perhaps compared to something like “rock health.” After all, rocks aren’t healthy or unhealthy; they’re just rocks. The most common perception among those working in production agriculture a few decades ago was quite similar when it came to soil: “It’s just dirt.”

Specific definitions have a lot to do with this perception. The actual soil particles—sand, silt, and clay—are neither healthy nor unhealthy on their own. It’s when these particles come together and form a soil ecosystem, one in which hundreds of millions of species live (it’s estimated that nearly 60% of all plant and animal species exist in the soil), that we can begin to apply an adjective like healthy.

Once we accept that soil health is a valid concept, the next logical questions follow: What does it mean for soil to be healthy? How can we measure it? And how can we influence it?

The metrics we use to judge the health of more familiar ecosystems—such as our own human environment—provide a useful starting point. Does the system function in a way that supports the life forms adapted to it? Many of these metrics apply to specific species, but it’s reasonable to assume that broader factors—air quality, water access and quality, and overall system function—are relevant across ecosystems.

Even when we narrow our focus to the health of a single species, there’s still ambiguity in how we define and measure health. In the human environment, should we look at population size, life expectancy, infant mortality, chronic disease, reproductive success, or something else entirely? The options are many. The same is true for soil health once specific ratings and tests come into play. What matters most is understanding the broad principles about which there is general agreement.

When we consider the health of an agricultural soil environment, its primary function is clear: to support robust crop growth, strong plant health, and high yields—while at least maintaining, and ideally improving, its future productive capacity.

One of the best predictors of this ability is the amount and activity of microbial life in the soil. Soil microbes support plant and root function through a symbiotic relationship in which they consume and convert organic and mineral soil components into plant-available nutrient forms. Microbes can dramatically expand the effective reach of plant roots within the soil profile, forming networks that move nutrients through the soil—as is the case with mycorrhizal fungi and phosphorus—and in some instances even delivering nutrients directly into plant roots.

These microbes are not a luxury for plants; they are essential. Without soil microbial life, plants could not exist. A healthy microbial population acts as a constant, season-long supplier of nutrients to growing roots.

The relationship is mutually beneficial. Plants continuously secrete root exudates composed of sugars, proteins, amino acids, and organic acids—the chemical products of photosynthesis. Roughly half of the energy produced through photosynthesis is converted into grain, while the other half is released through the roots to feed soil microbes. This energy source causes microbial populations to explode in the immediate vicinity of plant roots. Many microbial species complete their entire life cycle in a matter of days—or even hours—leading to dense populations very quickly.

The zone extending roughly two-tenths of an inch from the root surface is known as the rhizosphere. Within this zone, microbes not only consume root exudates but also convert mineral and organic soil materials into soluble, plant-available nutrients located precisely where roots can access them. The plant feeds the microbes, and the microbes feed the plant—a truly symbiotic system.

Microbes also play a critical role in other positive soil processes, including the decomposition of crop residue into organic matter and the formation and stabilization of soil aggregates. The health and abundance of microbial life is likely the single best indicator of a soil’s ability to function effectively in supporting crop growth. This is true not only because of what microbes do directly, but also because their presence reflects other essential soil conditions—such as good structure, adequate pore space for oxygen movement, proper drainage, and an environment that supports beneficial aerobic organisms while minimizing crop stress from saturated soils.

A healthy and abundant microbial population represents the best measure of soil health available today. It defines the biological component of soil health while reinforcing the chemical and physical properties that support plant growth. There are multiple metrics that can measure, or help infer, microbial activity and soil health, including organic matter levels, bulk density, porosity, and more advanced tools such as soil respiration tests.

While absolute standards that apply universally across all farms have yet to be established, the most important approach is adopting beneficial management practices and tracking results over time to verify improvements that support productivity.

Practices that promote healthy microbial populations include minimizing tillage, ensuring good drainage, keeping living roots in the soil for as much of the year as possible through cover crops, and—where feasible—applying manure. Halderman Farm Managers are keenly aware of how these practices impact soil health and work closely with tenants to maximize the benefits of their production plans while minimizing negative influences.

Healthy soil leads to excellent crop yields, which in turn produce the strongest return on investment for landowners. At the same time, the market increasingly recognizes the value of soil health, and farms with stronger soil health command higher prices per acre when sold. At Halderman, we seek sustainable ways to maximize your current income while enhancing the long-term value of your farmland investment.