(Tropical) soil organic matter modelling: problems and prospects

Soil organic matter plays an important role in many physical, chemical and biological processes. However, the quantitative relations between the mineral and organic components of the soil and the relations with the vegetation are poorly understood. In such situations, the use of models is an important research tool to explore the relations between the various components, to increase insight into processes, to examine the consequences of management, and to explore the possibilities for modification. An overview is given of the state-of-the-art in modelling of soil organic matter dynamics, with special emphasis on the processes in tropical regions. Major points identified as insufficiently developed include: Methodology is lacking to quantitatively describe the impact of soil texture and soil structure on the activity of soil biota. Effects of the microfauna on modelled organic matter transformations in the soil appear to be lacking. Techniques for direct measurement of pool sizes and characterisation of the relevant properties of the variety of organic substances would represent a major step towards verification of models and the revision of inherent concepts. The non-nutrient functions of organic matter, such as structural stability, water holding capacity and cation exchange capacity, need far more attention in modelling of soil organic matter. This revised version was published online in June 2006 with corrections to the Cover Date.