Soil health indicators

By James Hoorman, Hoorman Soil Health Services, and Jon Traunfeld, University of Maryland Extension

How do I know if my soil is healthy and what are indicators of soil health ?  Plants thrive in healthy soils and are not overtaken by pests (weeds, insects, diseases).  Weeds are the first colonizers of unhealthy, compacted or newly formed soils. Usually something is missing (soil organic matter (SOM), a certain nutrient, soil too tight) and weeds thrive under these conditions until the condition improves.  Insect and disease pest also thrive, because the plant is sick and easy prey.  Just like the lion or wolf in the wild, the sick and weak are consumed.

Jim Hoorman, Hoorman Soil Health Services

Healthy soils have deep loose soil for good root growth.  The soil should be dark in color meaning that the soil has plenty of SOM.  Healthy soil should be slightly moist, crumble,  have soil aggregates that fall apart, and have an “earthy” smell. When it rains, the aggregates should stick together and not turn to mud.  Soil that turns to mud in water is composed of mostly micro-aggregates.  When microaggregates become sticky and clump together they form macro-aggregates which allows our soils to crumble.  The glues in the soil from plant roots, biological life, and microbial wastes are what keeps our soils from turning to mud and also stabilize and keep soil nutrients plant available.

Use a shove to evaluate soil health by digging a hole 2-3 feet deep.  The longer it takes you to dig a hole and the more effort you have to exert, the more likely your soil health is poor.  Virgin healthy soils are easy to dig and have few if any compacted layers.  Water drains easily and does not pond on the surface or cause runoff, eroding valuable topsoil and nutrients.  The hardest part about digging in a healthy soil may be the proliferation of roots which keeps soil bound together.  However, when you shake the roots, the soil should crumble  into large stable soil peds which indicates you have many large macroaggregates.  The large peds (macro-aggregates) are stable and contain most of the SOM and plant available nutrients in healthy soils.

Soil biological life is the biggest indicator of good soil health. Soil should be full of earthworms, beetles, spiders, ants, and other soil life in the top six inches. Healthy soils generally have live plants growing year-round to feed soil microbes and other soil animals.  A healthy soil food web is a requirement for healthy soils.   Soil is not just inert clay, silt or sand; it is teeming with bacteria, fungi, and many other living organisms; comprising a living ecosystem. Only living things have “health” so when  we start thinking about “soil health”, we need to recognize that the soil is alive!  According to the USDA-NRCS definition, “Soil health is the continued capacity of a soil to function as a vital living ecosystem that sustains plants, animals, and humans.”

Almost all soils farmed long-term have been altered from their natural state. Most soils have become degraded due to a loss of SOM from excess tillage leading to soil compaction, soil erosion, and nutrient loss. When soil becomes compacted it is physically changed (less space between soil particles). This reduces root growth and the uptake of plant nutrients, and reduces biological activity, as soil organisms will have less oxygen and less room to move and reproduce (Traunfeld, 2020).

Improve your soil by increasing your SOM.  Diversifying crop rotations, adding cover crops, and enhancing your soil with reasonable amounts of manure while reducing excess tillage can restore soil function and soil health. Jon Traunfeld, University of Maryland Extension says, “Soil is a living  ecosystem that can be managed to provide nutrients for plant growth, absorb and hold water, filter and buffer potential soil nutrients from leaving our fields, and provides habitat for soil microbes to flourish and diversify to keep the ecosystem running smoothly.”

To improve your soil health, follow these USDA-NRCS four soil health principles.  First, minimize soil disturbance or tillage to maintain and improve SOM.  Second, maximize surface residue to absorb the impact of rain drops and to insulate the soil from extreme temperatures.  Third, maximize live roots in the soil to create good poor space, to add SOM, to allow water to infiltrate and be stored, to feed the microbes, and to absorb and recycle soil nutrients.  Then add biodiversity by rotating crops to create a healthy food web and healthy soils. The best opportunity to improve your soil health is to start in the fall, by reducing tillage and growing a cover crop.

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