Testing soil quality | WWF

Testing soil quality

Soil quality is simply defined as "the capacity of a specific kind of soil to function", i.e. mainly to provide nutrition to plants and absorb and drain water. The different properties of soil are - texture, moisture, fertility (level of nitrogen, phosphorus, potassium) and pH level. The pH is the measure of a soil's acidity or alkalinity.
Each of these properties depends on different factors. For example, soil moisture depends on climate, topography and other soil characteristics. The temperatures of soils vary depending on their water holding capacity. Soils with low water holding capacity are warm.

We should know which type of soils have more or less water holding capacity so that we can use the soil best suited for a particular plant. Moreover, using the right type of soil for gardens and farms and for sewage systems ensures that there is no wastage of water or unnecessary flooding because of unsuitable soil.

For example, when installing sewage systems or building a road, it is important to use soils with less water holding capacity that allow fast drainage. Similarly, plant growth depends on the amount of organic matter present in a soil and we should check the soil for fertility and humus to avoid the use of artificial fertilizers.

Knowing the quality of soil helps in different ways:
  • Tests help to pick the most suitable plants for the soil - which is usually more ecologically sound and less costly
  • It helps determine whether the soil needs amendments or more manures to make it suitable for growing plants or crops
  • It can help make informed decisions about how much water to use and how to plan out the garden or farm area.

Testing soil quality

When measuring soil quality, we should evaluate the physical, chemical, and biological properties of the soil. Physical properties include texture, water content, infiltration rate, aggregate stability, slaking, and morphological estimations. Biological properties include soil respiration and earthworms. Chemical properties include pH, electrical conductivity (EC), and soil nitrate levels. You can test different properties of soil. Here are some simple tests:

Fill one third of a jar with the sample soil. Add one-third volume with water. Shake the jar vigorously and let it settle overnight. The coarse sand particles will settle first followed by the silt and then the clay.

Moisten some soil or take some moist soil in your hand. Squeeze it and then open your hand. If the soil holds together (that is, forms a cast) then it has a higher percentage of clay.

In your garden, identify areas where water tends to accumulate and where it tends to drain rapidly. Compare plant growth in different areas. Thick lush growth indicates high moisture while sparse growth indicates less moisture in the soil.

Take a sample of soil that is at least I foot deep from the surface. Check its colour. If it is dark then it has humus, which means it is fertile. If it is light in colour, then it is not that fertile.

A simple test is to check the soil for texture and for humus. The more humus and clay there is, the more fertile the soil.

You can also conduct chemical tests to determine pH levels and soil quality.

After you get the results, suggest what type of plants are best suited for the soil and what kind of slope, watering system will it need.