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, physical, chemical and biological. The geometry and dimensions of the pore space define the rates at which such processes occur. Using relatively simple structures, generated from the desiccation of soil slurries, we investigated the action of adding a range of substrates to the soil (e.g. glucose or ammonium nitrate), in relation to emerged cracking patterns and soil stability. Using probability and Monte Carlo techniques, we quantified the heterogeneity and connectivity of the cracking patterns. We hypothesise that the addition of substrates directly acts to alter microbial activity which then alters the cracking patterns of dried soil slurries. In addition, we show that 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 created during desiccation and decreased the stability of cracks (P < 0.05). The mechanisms controlling these effects are discussed.