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Sponsored: Three Sides to Every Soil
One hot summer afternoon in 2013, I parked in a waterway after scouting a large soybean field and made a phone call to a respected professional colleague.
“Peter, does it seem to you like soil appears to be more played out these days? It doesn’t seem as alive, rich in color, or have that fresh earth smell. When I walk on it, it feels like concrete not a garden. Soybean root and plant growth seem slow, and nodule formation is weak for the growth stage.”
That began a lively discussion between two dirt nuts. We covered it all: how the weather cycle we’d experienced ‑ two years of excessive water followed by a severe drought ‑ was affecting the soil; how fields with more organic matter and fertility survived environmental stresses better than those with less; and finally, the consideration that even the “lifeless” soil I thought I was walking on was really teeming with millions of microbes per cup of soil.
We agreed on one critical assessment ‑ the soils we farm can be better. Anything we can do to increase the organic matter content of this precious resource will result in a corresponding increase in and protection of its productive function.
We measure the health of biological systems by their ability to perform certain required or desired functions. Human beings need to be able to eat, work, reproduce, think, and create. Soil is no different. It needs to filter and store water, sustain plant and root growth, hold nutrients, exchange gases with the atmosphere, insulate, and produce food to feed countless beings. When one or more of these desired functions is compromised, the root of the problem often originates in the degradation of some component of the system’s health.
Soil is composed of five primary constituents: mineral matter, water, air, organic matter, and living organisms. Think of soil as a triangle with three functional sides to it ‑ chemical, biological, and physical ‑ with soil organic matter as the central soil property of that triangle. Soil organic matter content is at the very core of a soil’s health and productive function. The organic fraction of soil is the part of it that feeds the living organisms performing critical functions, improves soil structure and aggregate formation, and stores and cycles nutrients critical to crop growth and development.
There are different indicators we can look at for each side of the triangle:
Physical: aggregate stability, water infiltration and storage, structure, porosity
Chemical: organic matter content, cation exchange capacity, potassium, phosphorus, pH, nitrogen
Biological: microorganisms and respiration, earthworms, enzymes
In production agriculture, we tend to focus more heavily on the chemical side of the triangle because the more routine soil testing and measurement techniques were developed primarily for chemical properties. We’re also more conditioned to see how crops respond to management practices like liming and fertilizer application.
But we’re missing a key element when we view soil health only through a chemical lens. The physical and biological considerations are equally important when assessing soil health.
Here’s what you can do to be proactive:
1. Similar to soil testing for pH or phosphorus concentration, use one or two fields as a baseline to measure information with respect to soil aggregate stability, earthworm populations, or respiration and water infiltration rates.
2. Use physical and biological baseline measurements to evaluate management practices that increase organic matter content, like reduced tillage, manure application, introduction of cover crops, bringing wheat back into the rotation, and frost-seeding clover into wheat. Measure how these practices positively or negatively impact soil physical and biological indicators and grain crop yield.
Most importantly, think in three dimensions. Realize that we farm cubic feet of the most precious resource on earth, not just acres.
-David Hughes, CCA | Field Agronomist