Tillage, particularly of virgin lands, can lead to immediate and short-term increases in microbial biomass and metabolism. On the other hand, soil mesofauna may decline. Earthworms are often adversely affected, but not always. Incorporation of crop residues disperses microbial activity to a greater depth than is seen in reduced-tillage systems. The latter show aerobes, facultative anaerobes, and nitrifiers concentrated in the surface strata.
Tillage also affects the composition of bacterial communities.
Agricultural burning leads to loss of organic matter and the liberation of P and other cations. Soil pH increases, and there are often increases in soil microbes, N mineralization, and nitrification, although nitrifiers and N availability can be reduced. Burning is often accompanied by tillage, so effects are often compounded, or confounded, in practice. Tillage of virgin lands causes slow decline in soil organic matter. The scientists postulated the existence of a persistent and a labile fraction of the total soil carbon.