What do we mean by “soil health” and how can we pursue that goal? When I was pursuing my degrees in the Vegetable Crops Department at Cornell my two minors were entomology and soils. I was always fascinated by different soils types and was lucky to experience a variety of soils during my career, from Howard gravelly loam soil in New York to the Norfolk sandy loam soil of eastern North Carolina to the Haynie very fine sandy loam soil in Kansas to the Hagerstown silt loam at the Penn State Research Farm.
A farmer’s soil is fundamental to producing a crop and can be described as a bank account: the farmer makes withdrawals and at the same time makes deposits to maintain a positive balance. The soil bank account concept will work only if you make deposits by using management practices that improve soil health and increase productivity and profitability both now and in the future. A healthy soil produces the maximum amount of products at the least cost. Maximizing soil health is essential to maximizing profitability.
How do we keep our soils healthy? It’s mostly a matter of maintaining suitable habitat for the myriad organisms that comprise the soil food web. This can be accomplished by four overarching principles: disturbing the soil as little as possible, growing as many different species as practical, keeping living plants in the soil as often as possible and keeping the soil covered all the time.
Soil can be disturbed through physical, chemical or biological activities. Physical soil disturbance, primarily through tillage, results in bare and/or compacted soil that can be destructive and disruptive to millions of soil microbes. Some farm inputs can be disruptive to the symbiotic relationships between fungi, microorganisms and plant roots. According to soil scientists, all forms of soil disturbance diminish habitat for soil microbes and result in a diminished soil food web.
Plants use sunlight to convert carbon dioxide and water into carbohydrates that serve as the building blocks for roots, stems, leaves and seeds. Plants interact with specific soil microbes by releasing carbohydrates or sugars through their roots into the soil to feed microbes in exchange for nutrients and water. Through research by soil microbiologists, we know that diverse plant carbohydrates are required to support a diversity of soil microorganisms. We can achieve a high level of diversity of plant carbs by growing a variety of plants. The key to improving soil health is ensuring that food and energy webs consist of several types of plants, not just one or two.
Biodiversity is ultimately the key to the success. When biodiversity is lacking it severely limits the potential of any cropping system and increases the potential for disease and pest problems. A diverse and fully functioning soil food web provides for nutrient, energy and water cycling that allows soil to reach its full potential. Increasing the diversity of crop rotations and cover crops increases soil health and the proper functioning of the soil, thus reducing input costs and increasing profitability.
All living plants maintain a rhizosphere, an area of concentrated microbial activity close to the roots. Scientists say it’s the most active part of the soil ecosystem because it’s where the most readily available food is, and where peak nutrient and water cycling occurs. Soil microbiologists note that healthy living roots provide the easiest source of food for soil microbes, so growers can provide food to the microbes by growing long-season crops or a cover crop following a short-season crop. Sugars from living plant roots, recently dead plant roots, crop residues and soil organic matter (SOM) all feed the many and varied members of the soil food web.
Keeping soil covered conserves moisture, reduces soil temperature, intercepts raindrops (reducing their destructive impact and preventing runoff), suppresses weed growth and provides habitat for members of the soil food web that spend at least some of their time above ground. Keeping soil covered while allowing crop residues to decompose allows nutrients to be cycled back into the soil. It’s important that growers consider their crop rotation, including any cover crops and residue management, to keep soil covered and feed microbes at the same time.
Farmers should always look toward enhancing SOM. To improve SOM, use diverse, high biomass crop rotations, cover crops and reduced tillage. Growers increasing surface residue can form a physical barrier to wind and water erosion. It should be noted that higher crop residue rotations and cover crops contribute more SOM and nutrients to the soil. Less soil disturbance also means lower organic matter losses. Improving SOM will improve the structure of soil, which becomes more stable and less prone to crusting and erosion; water infiltration increases and runoff decreases when soil structure improves. Beneficial soil organisms become more numerous and active with diverse crop rotations and higher SOM levels.
Increasing SOM increases soil aggregation and decreases runoff and improves ground and surface water quality because of better soil structure, infiltration and biological activity – making the soil a more effective filter. Crops are better able to withstand drought when infiltration and water holding capacity increase. By increasing SOM, growers may see less disease organisms, which could reduce the need for pesticides. The health of your crop and its vigor may increase when soil biological activity and diversity are increased.
Soil health cannot be determined by measuring only crop yield, water quality or any other single outcome. Since we cannot measure soil health directly, we must evaluate indicators that are measurable properties of soils or plants that can provide clues about how well the soil is functioning. The indicators that we can measure are physical, chemical and biological properties, processes or characteristics of soils. We can also look at morphological or visual features of plants. SOM is an important indicator of nutrient retention and soil fertility, structure, stability and erosion. Physical measurements can be made on bulk density, infiltration, soil structure and macropores, soil depth and water holding capacity (an indicator of retention and transport of water and nutrients), habitat for soil microbes, estimate of crop productivity potential, compaction, plow pan, water movement, porosity and tilth.
Chemical measurements can be made on the electrical conductivity, reactive carbon, soil nitrate, pH and extractable phosphorus and potassium (which can be indicators of biological and chemical activity thresholds), plant and microbial activity thresholds and plant available nutrients (and potential for N and P loss). Biological measurements on the number of earthworms, microbial biomass, particulate organic matter, potentially mineralizable N, soil enzymes, soil respiration and total organic carbon are all indicators of microbial catalytic potential and repository for C and N, soil productivity and N supplying potential and microbial activity measure.
Maintaining soil health has certain principles and practices that need to be followed, just like a program for maintaining human health.
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