Soil health is the capacity of soil to function as a vital living system to sustain biological productivity, maintain environmental quality, and promote plant, animal, and human health. This is a concept that characterizes the ability of a living soil system to perform functions such as supporting plant health. 

The idea of a healthy soil must be conveyed through useful measurements known as soil health indicators that are sensitive to changes in soil processes and represent connections between soil biological, chemical, and physical properties. 

There are three types of soil health indicators:

Chemical Indicators

  • pH: pH is an important indicator of soil health because if there is inadequate soil pH, crop growth can be impacted and key nutrients may become less available. Additionally, soil pH can vary soil microbial communities.
  • Macronutrients: N, P, K, Ca, Mg, S are all macronutrients that are vital to plant growth. If these nutrients are not available in plant usable quantities, crop growth will likely suffer.
  • Micronutrients: Although necessary in smaller quantities than macronutrients, micronutrients are just as critical to plant growth. Typically, soils provide plants with enough necessary micronutrients.  

Physical Indicators

  • Aggregate Stability: Soil aggregates that are held together tightly via root exudates, soil fungi, and inherent soil properties. They can be improved upon by creating environments for “biological glues” to be produced by plants and microbes by reducing tillage that physically breaks soil aggregates.
  • Available Water Capacity: Much of this depends on innate soil texture but can be impacted by the amount of soil organic matter and soil aggregation, both of which can increase water holding capacity.
  • Soil Compaction: High amounts of soil compaction mean less room for air or water in the soil, impacting water infiltration and drainage, plant root growth, as well as soil microbial communities. Being timely when driving large equipment on soils, as well as implementing deep rooting plants on the soil, can help alleviate this.

Biological Indicators

  • Soil Microbial Protein: Measures nitrogen from proteins being broken down in the soil which would then be available for plant uptake.
  • Active Carbon: Measures the carbon-containing compounds which are readily broken down by microbes as food. Active carbon is essentially a measure of the food stock available for microbes, which promotes nutrient availability and cycling.
  • OM: Organic matter influences water holding capacity, contains nutrients that can be broken down and made available, and provides food for microbes. Improving organic matter in the soil can be challenging but made easier by introducing conservation tactics like reducing tillage, adding other crops to a rotation, and using cover crops.
  • Respiration: Measures the amount of CO2 produced by microbes which can help indicate soil microbial activity.