Our first soil health assessment was conducted at the Tree Fest site at Kentucky.
The process to conduct a soil health assessment:
The process involves a 50 metre transect with measurements taken in 5 random quadrats at 10 metre intervals. A 20 cm cube is dug within the each 50 cm quadrat.
- Measuring groundcover: the % groundcover of the quadrat is measured, which includes living and dead plant material, dung and rocks. The more groundcover the better. Groundcover prevents soil erosion by slowing down the flow of water. Litter provides a food source for decomposer organisms, which contributes to nutrient cycling and soil organic matter formation.
- Infiltration measurement: using a piece of PVC pipe, measure how long it takes for 500ml of water to enter the soil. This indicates how well water can enter the soil system for plant production benefits, rather than creating run-off which can cause erosion.
- Penetrometer: a small piece of 3mm wire is used to test how easy it is to penetrate the soil. It acts as an indicator of compaction, which can prevent root development and water infiltration.
- The clod of soil is dropped on to a board to look for aggregation. Aggregates are small clumps of soil particles (sand, silt and clay) and organic matter held together by chemical, physical and biological activity. Aggregates provide good soil structure and act as an aerated habitat for soil organisms as well as allowing for water storage and movement.
- A slaking and dispersion test is conducted with small soil samples from 10 cm and 20 cm depth to check for aggregate stability.
High scoring of slaking is where the aggregates don’t collapse in the water (indicating good soil structure).
High scoring of dispersion is where there is minimal clouding of the water (indicating no sodicity).
- pH of Soil: pH measures the concentration of Hydrogen ions in the soil. There is natural variation of pH within soils, which can range from 5.5 (acidic) to 8 (alkaline). However, a good score would range between 6 and 7.
- Measurement of average root depth. The roots help with aggregation by providing a food source for microbes. The deeper the root depth the more opportunity for building soil structure deep into the soil profile, which increases water-holding capacity and nutrient availabilty, thus increasing plant production and the development of topsoil.
- Prevalence of root volume: Take 10 aggregates from the 10 cm level and 20 cm level of sample and check for the presence of roots. Root presence in aggregates demonstrates the volume of topsoil being developed across the soil profile.
- Soil organisms: Soil organism diversity is measured by counting how many different organisms are in the 20cm cube of soil, such as earthworms, beetles, ants and spring-tails. Organisms visible to the human eye are higher up in food chain of the soil food web (ie they eat the smaller organisms we cannot see), as well as helping to break down organic matter which becomes a food soils for smaller organisms. They play a critical role in nutrient cycling and soil organic matter formation.
- Rhizosheath measurement: The rhizosheath is the area around the root that provides a favourable environment for microbial activity and root growth. They look like root dreadlocks.
- Ribbon Test: To test for the soil texture and level of clay in the soil.
- Aggregate Profile: Looking at aggregate profile over the 20 cm depth. A well aggregated soil contains mostly micro-aggregates (small, fine clumps of soil). Large, solid clods of soil indicate compaction.