This document discusses soil microbial ecology and the role of microorganisms in soil. It notes that different microhabitats in soil favor different indigenous microbial populations. Soil particles provide microenvironments with decreasing oxygen levels from the surface. Indigenous soil microflora are determined by abiotic soil factors and some have adaptive structures like endospores. Soil microorganisms play important roles in biodegradation, mineral cycling like nitrogen fixation, and biogeochemical cycles.