Links between substrate additions, native microbes, and the structural complexity and stability of soils

Soil pore space influences and controls a vast array of soil processes, phy sical, chemical and biological. The geometry and dimensions of the pore spa ce define the rates at which such processes occur. Using relatively simple structures, generated from the desiccation of soil slurries, we investigate d the action of adding a range of substrates to the soil (e.g. glucose or a mmonium nitrate), in relation to emerged cracking patterns and soil stabili ty. Using probability and Monte Carlo techniques, we quantified the heterog eneity and connectivity of the cracking patterns. We hypothesise that the a ddition of substrates directly acts to alter microbial activity which then alters the cracking patterns of dried soil slurries. In addition, we show t hat the addition of substrates acted to decrease crack heterogeneity (1.30- 1.47), and increase crack connectivity (1.15-1.27) and density (10-16%), (P < 0.05). The addition of glucose decreased the number of aggregates create d during desiccation and decreased the stability of cracks (P < 0.05). The mechanisms controlling these effects are discussed. (C) 1999 Elsevier Scien ce Ltd. All rights reserved.