Soil management is known to affect microbial populations relevant to nutrient cycling and plant health. We investigated the effects of several cropping management practices on a Central Queensland vertisol, including the application of liquid biological inoculums, green manuring and conventional chemical fertiliser. Soil microbial load and diversity was indexed using soil respiration, Biolog Ecoplate and FF microplates and PCR-DGGE. Compared to cultivated soil, uncultivated vertisol, represented by virgin brigalow soil, possessed 87% higher soil nitrate than cultivated soils, and significantly higher microbial catabolic potential, as observed in Biolog substrate utilisation patterns. In cultivated soil, there was little difference between treatments in these substrate utilisation patterns, but large changes associated with season. However, the results of 16S rDNA and Internal Transcribed Spacer region based DGGE profiles were consistent with an increase in bacterial diversity and a decrease in fungal diversity in amended cultivated soils relative to the unfertilised cultivated treatment.
