Summary Many mathematical description of C and N transformation in soil have been developer in the last decade but only a few explicitly model the activity and mass of soil organisms. Great difficulties still exist in establishing basic parameters governing the kinetics of microbial turnover. The present state of the art is discussed briefly
The model of Van Veen and Frissel on C transformations and related mineralization and immobilization of N has been developed further based on laboratory and field data obtained with different Australian soils. Firstly case studies show the large effects of the frequency of drying and rewetting of soil on the decomposition of organic matter and on the turnover of biomass. Secondly the more refined model embraces the concept that soils have characteristic capacities to preserve both organic matter and microorganisms. Perservation of microorganisms could result from protection against predation and from amelioration of harsh environmental conditions. Biomass formed in excess of a soil preservation capacity is assumed to die at a relatively high.Furthermore biomass and its immediate organic products of decay are considered to form mainly a closed system from which only small proportion of the products leak out as stabilized materials.