New Soil Health Measurements

By James Hoorman, Hoorman Soil Health Services

The Soil Health Institute (SHI), a non-profit organization dedicated to enhancing soil productivity, recently announced results from a 3-year research project on identifying soil health measurements across North America.  Over 100 scientist reviewed data from 124 sites in Canada, Mexico, and the United States; comparing conventional tilled farming systems to long-term no-till, cover crops, and perennial cropping systems. 

Over 30 key soil health measurements were taken at various research sites in this project.   Measurements were taken across a wide range of climates, soil types, environmental conditions, cropping practices, and different management. Scientifically, evaluating that many sites and that much data gave the project the scientific rigor to valid these soil health measurements across many different systems. 

Evaluating soil health is all about how well soil’s function.  Functions such as water, carbon, and nutrient recycling are important for good plant productivity.  Healthy soils are able to absorb and store water, so after a heavy rain, water easily infiltrates the soil and does not run off.  Also, healthy soils hold more water and more plant available nutrients, which improves water quality.  Healthy soils keep the soil, water and nutrients on the land; so there is less nutrient and soil loss from soil erosion.  A side benefit, it also keeps the micro-nutrients in the soil so plants, animals, and humans consuming these nutrient-rich plants are healthier.  Healthy soils, create healthy plants, and the animals and humans that consume these products are also healthy. 

It’s a simple and beautiful cycle, but it can easily be broken. Farmers can manage their soils to improve soil health; but farmers need effective, easy to use, practical, and  relatively inexpensive measurements to evaluate their progress and to make positive soil health changes.  Based on these criteria, the SHI identified three (3) major measurements that can be used in North America to measure soil health long-term.  These three measurements  are 1) soil organic concentration (soil carbon), 2) carbon mineralization (how soil nutrients recycle), and 3) aggregate stability (related to soil structure and reducing soil compaction).  These three measurements relate directly long-term soil health.   

Soil carbon is the carbon in soil organic matter and influences water and nutrient holding capacity,  microbial and plant diversity,  and many other key soil properties.  Carbon mineralization is all about how well the microbial community functions in both releasing and tying up soil nutrients.  Healthy soils have more soil microbial diversity and resilience to climatic and environmental changes.  Aggregate stability relates to how strongly soils group together.  Healthy microbes and root exudates supply the carbon and sugars to bind soil together so that it crumbles.  It enables the soil to breathe and allows both air and water to move easily within a soil.  A lack of soil aggregation leads to dense compacted soil without good soil structure, leading to poor plant and microbial growth.  Poor aggregate stability leads to water runoff, less water infiltration, soil erosion, nutrient runoff, and poor water quality.

From a research stand point, one other measurement was found to be extremely helpful.  Soil texture or the amount of sand, silt and clay in a soil is a factor that is helpful in measuring a soil’s water holding capacity.  Since this measurement does not change much over time, it needs to be measured only once, and is often readily available, based on soil survey maps.  (Source Soil Health Institute (SHI)).

To improve soil health, there are four principles that need to be followed.  First, minimize soil disturbance or tillage.  When soils are tilled, soil carbon is lost from the soil within minutes due to the excess oxygen which rushes into the soil.  Excess oxygen pushes out soil carbon dioxide but also increases microbial respiration or release of stored soil carbon in soil aggregates.  Second, maximize live roots in the soil.  Roots are the source of the majority (80-85%) of soil carbon.  Tilled soils have roots growing only 4-5 months while no-tilled soils with cover crops or perennial crops have live roots growing year-round. This carbon feeds soil microbes, it improves aggregate stability, and its where most soil carbon and soil nutrients are stored.

A third principle, is to maintain surface residue.  Surface residue is like a blanket on the soil in the winter, keeping the soil temperature warmer and like an umbrella in the summer, keeping soils cooler.  This umbrella or blanket (soil residue)  also minimizes soil erosion and nutrient loss.  Fourth, improve soil diversity by using good crop rotation with many diverse plants (cover crops) with diverse roots (deep vs shallow, tap roots vs fibrous), and diverse microbial populations. Improving soil health is an efficient and profitable farming practice that is also good for the environment.     

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