ABSTRACT
In high-productivity agricultural ecosystems, natural soil fertility is commonly supplemented by applications of nutrients, either as inorganic fertilizer or organic manures, and occasionally both. However, the activities of the soil micro-organisms (collectively the soil microbial biomass) in decomposing plant and animal residues and in the formation and mineralization of soil organic matter still underpins the fertility of these managed systems. In natural ecosystems these natural processes determine, almost entirely, the fertility of their soils. Any decline in natural soil fertility will therefore have disproportionately large effects in natural systems but still cannot be ignored in managed ones. The soil-plant ecosystem may be damaged, either in the long-or short-term, by agents that inhibit or stop the natural functioning of the soil micro-organisms.
