The soil ecosystem - its natural (normal) status, functioning and resilience
As GMM applications in (agricultural) soil will undoubtedly be important, a special focus is placed here on the intricacies of the agricultural soil environment, in particular its quality and health status. This soil status is important as the following indispensable functions are supported:
- 1. the availability of plant nutrients (soil fertility)
- 2. the suppression of soil-borne plant diseases (see Chapter 2; Kennedy and Smith, 1995)
- 3. the cleaning function of soil, e.g. for the provision of clean drinking water (by filtering and biodegradation).
These three functions are known as the life support functions (LSF) of soil. They are very tightly linked to, and dependent on, crucial constituents of the soil microbial community. This section will briefly touch upon the first two functionalities.
Nutrient cycling function of soil
Soils are responsible for a large part of the nutrient cycling processes (i.e. the cycling of different forms of carbon, nitrogen, phosphorus and sulfur) that drive ecosystem functioning on Earth. As examples, key steps in the nitrogen cycle such as nitrogen fixation, ammonia oxidation and denitrification, are carried out by micro-organisms that inhabit soils. In particular, ammonia oxidation and denitrification in soil determine what chemical forms of nitrogen, ammonium, nitrite or nitrate, will be available in (ammonium), or are flushed out (nitrate) of soil. Both processes are driven by several microbial groups, with the connotation that ammonia oxidation (carried by a few groups mainly among the beta-Proteobacteria and archeae) is less broadly spread than denitrification (carried by many groups across the bacterial domain).