Fungal to bacterial ratio
The fungal to bacterial ratio (F:B ratio) is the ratio between the total fungal biomass and the total bacterial biomass in a soil. Natural ecosystems have specific soil f:b ratios. These depend on various factors, such as the type of vegetation, the rooting density, soil moisture, soil type, the average annual temperature and the average precipitation in an area (He et al., 2020). Disturbed soils, such as agricultural land, are generally highly bacterial. This is because agricultural practices such as ploughing damage fungi much more than bacteria.
Plants that colonize bare soil quickly (those we commonly refer to as weeds) generally require highly bacterial dominated soils. (Weeds therefore often grow well in agricultural fields.) Most types of grasses and vegetables require more fungi. Perennials generally require even more fungi, and trees require the most fungi, and therefore the highest F:B ratios. A high weed density can be a sign that the F:B ratio is too low for the plants that are grown in a (agricultural) field.
The f:b ratio determines what forms of nutrients will be available to plants. In a soil where bacteria predominate, plant available nitrogen is mainly released in the form of nitrate. In a soil where fungi predominate, plant available nitrogen is mainly released in the form of ammonium. Generally, it can be said that woody plant species (mainly trees, shrubs and vines) require more ammonium, while herbaceous plant species (mainly annual, biennial and perennial herbaceous plants) require more nitrate. Less disturbed soils have higher fungal biomass, and therefore have higher fungal to bacterial ratios. This is because fungi are more sensitive than bacteria to soil disturbance.
The F:B ratio of a soil determines which form of nitrogen becomes available to plants. In a bacterial dominated soil plant-available nitrogen is mainly released in the form of nitrate. In a fungal dominated soil plant-available nitrogen is mainly released in the form of ammonium. In general, it can be said that woody plant species (trees and shrubs) require mainly ammonium, while herbaceous plant species (green plants with little or no woody tissue) require mainly nitrate.
Explanation of the score
The F:B ratio on your scorecard is based on the fungal and bacterial biomasses that were measured in your soil sample. An F:B ratio of 0,5 means there is two times more bacterial than fungal biomass in your sample. An F:B ratio of 1 means the fungal biomass equals the bacterial biomass. An F:B ratio of 10, means the fungal biomass is ten times the bacterial biomass, and so on.
Since there is no consensus in science about target values for F:B ratio in different land use and agricultural systems, the F:B ratio in your soil sample cannot be valued, rather it can be considered as an indication of the successional state of your soil. It can be interesting to monitor the F:B ratio in a field, for example when changes in soil management practices are made.