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.
The ability of a simulation model to describe accurately not shot-term events N cycling during one growing season but also the same processes over say a decade is an importent critertion in assessing its predictive power. In this paper some of the results will be discussed of testing the model developed from a consideration of the aforementioned laboratory studies for its accuracy in describing the decomposition of plant residues in an 8 yesr field experiment.
During the past decade many simulition models have been developed to describe the cycling of nutrients especially N in soil. Frissel and have classified soil N models according to their purpose dynamics and concept. Scientific models which have been developed to better understand the mechanisms of coupling of N transformation processes may be divided into three groups those in which