Land management practices that conserve and enhance organic matter and soil organisms will help sustain soil health. Organic matter stabilises soil structure by binding particles together to form aggregates, which reduce erosion and provide a habitat for soil organisms.
During organic matter decomposition, micro-organisms may tie up soil nutrientstcmporarily, which would otherwise be leached or eroded from the surface layers. The decomposition rate and therefore nutrient availability is determined by the carbon-to-nitrogen ratio of the organic matter and the activity of soil organisms. Organic matter with a high C:N ratio is usually less degradable because of its high level of complex molecules.
A lot can be learned about the dynamics of organic matter by examining the active fractions of plant residues. The active fraction includes the partially decomposed light fraction, which might still resemble sections of stems or roots. The total amount of organic matter in soil changes very slowly.(many farmers have noticed the carbon percentage in their soil samples does not change significantly from year to year).
The level of soil organisms is sometimes used to indicate changes in the active fraction of soil because they are sensitive to changcs in their environment.