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Author: Dr. Jennifer Wells
What is the definition of soil health?
Healthy soil is fundamental for profitable, productive, and environmentally sound agricultural systems. The definition of soil health is very much like the definition of “sustainability” where it can vary greatly, depending on who you ask. In agriculture, soil health most often refers to the ability of the soil to sustain agricultural productivity and protect environmental resources. Another definition is the improved function in terms of crop yield response to inputs, such as fertilizer efficiency.
Recently, Federal and State agencies have been working together to create a standard definition. To that end, the United States Department of Agriculture’s Natural Resources Conservation Service defines soil health as “the continued capacity of soil to function as a vital living ecosystem that sustains plants, animals, and humans.”
How is it measured?
Soil health cannot be measured by only looking at crop yield, water quality, or any other single data point. It must consider many different factors. One-way growers have evaluated their soil health in the past is by utilizing the “soil your undies” method. Yes, you read that right… ”soil your undies”. In this method, you take a pair of 100% cotton underwear and bury it 3” to 6” below the soil surface. After 60 days, dig up your underwear and evaluate the condition they are in. If they are still fairly intact, your soil health is less than favorable and there are a number of things you could do to improve it. If there is not much left but the waistband, your soil is pretty healthy. A healthy soil is full of organic matter, bacteria, fungi, arthropods, protozoa, and earthworms. Since 100% cotton is a food source for the microbes and other organisms in the soil, the worse looking the briefs, the more biological activity you have in your soil. Biologically active soil is healthy soil.
While this method is fun and does give an indication about soil health, there are other ways to evaluate it that give us more precise and detailed information. Evaluating soil health requires utilizing measurements of 3 different soil health indicators, which are chemical, physical, and biological. All are equally important. Chemical indicators look at factors such as pH, macro and micronutrients. pH can impact nutrient absorption by plants and microbial communities. The availability of macro and micronutrients in the soil are important for healthy crops. Physical indicators include aggregate stability, water holding capacity and soil compaction. Soil aggregates are groups of soil particles that bind to each other more strongly than to other particles. Aggregate stability measures the ability of soil aggregates to remain bound together when tillage and water or wind erosion are applied. Water holding capacity is generally innate to the soil type but can be impacted by the amount of soil organic matter and soil aggregation, both of which can increase water holding capacity. Finally, high soil compaction means less room for air or water in the soil, impacting water infiltration and drainage, plant root growth, as well as soil microbial communities. Biological indicators are soil microbial protein, active carbon, organic matter and respiration. Soil microbial protein measures the amount of nitrogen from proteins being broken down in the soil which would then be available for plant uptake. Active carbon measures carbon-containing compounds already broken down by microbes. Organic matter measures the amount of water holding capacity and food available for microbes. Finally, respiration measures the amount of CO2 produced by the microbes.
If all these tests seem to be overwhelming, but the underwear test seems too simple (and time consuming), utilizing the Truterra Sustainability Tool will help you understand more about your soil health and how you can improve it. Looking at your stewardship score card can give you an idea of how healthy your soil is today and running scenarios will help you make a plan for both short and long-term improvement. The soil quality trend score in our key performance indicator section indicates the predicted trend in gains, losses, or maintenance of soil organic matter and soil carbon based on current field operations and crop management. Utilizing the Truterra™ practice navigator section can give you some understanding of costs involved in implementing new practices and what could be available from NRCS funding opportunities. If you need more information on how to interpret your score card or run scenarios, reach out to your local Truterra account manager.
Why is soil health important?
Healthy soil offers many benefits to agricultural producers, including increased yield with reduced inputs such as energy, water, and nutrients. Healthy soils are aerated and have much better soil structure and biology. These soils drain quickly where fields degraded by tillage and residue removal lack drainage capacity. In healthy soils, water permeates down into the subsoil. In degraded soils, water pools at the surface and soil takes longer to dry out and warm up. With poor drainage and soil structure, farmers often have to wait longer for good weather and have shorter windows of opportunity to get into the field. In addition, improving soil health can offer many broader benefits such as improving water quality, reducing water use, increasing carbon sequestration in soils, reducing greenhouse gas emissions, storing water, and helping make land more resilient to climate change.
How to improve soil health?
The USDA Natural Resource Conservation Service (NRCS) has identified four basic principles to help growers improve their soil health. I referenced these in last month’s blog post, but they are important enough that they bear repeating. These are:
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