Microbiological aspects of soil structure

Summary A simple experimental model has been devised to study the effects of organic amendments on aggregate stability and microbial activity in the soil. In the two soils investigated the different organic materials used all produced increases in aggregate stability but significant differences were observed both in the magnitude and time of the increase attributable to individual treatments. Microbial activity, as assessed by visual techniques, was broadly correlated with the changes in aggregate stability though the different treatments tended to produce their own characteristic patterns of colonization. It was generally difficult to relate changes in aggregate stability with the activity of specific micro-organisms but in the case of samples treated with glucose and cellulose, yeasts were the dominant organisms. These have subsequently been shown to produce substantial quantities of an extracellular polysaccharide which is effective in bringing about aggregation.