EVALUATION OF SOIL BIOLOGICAL PROPERTIES AS POTENTIAL BIOINDICATORS OF SOIL HEALTH

Two long-term field trials in South Australia were used to detect and characterise changes in soil biological properties that were a consequ ence of different agricultural management. The properties examined wer e total bacteria, fungi, and actinomycetes; total pseudomonads; cellul olytic bacteria and fungi; mycorrhizal fungi; plant root pathogens (Ga eumannomyces graminis var. tritici, Rhizoctonia solani, Pythium irregu lare); bacterial-feeding protozoa; soil mesofauna (collembola and acar i); earthworms; microbial biomass; C and N mineralisation; in situ CO2 respiration; cellulose decomposition; acid soil enzyme activity (pept idase, phosphatase, sulfatase). The sensitivity of these biological pr operties was assessed to tillage (no-tillage v. conventional cultivati on), stubble management (stubble retained v. stubble harvested), crop rotation (continuous wheat v. wheat-sown pasture), and N fertilisation (nil v. 80 kg N/ha applied during the crop phase). Tillage, stubble m anagement, crop relation, and N fertilisation significantly (P<0.01) a ffected C mineralisation and microbial biomass. Tillage with stubble m anagement significantly affected root pathogenic fungi, protozoa, coll embola, earthworms, and cellulose decomposition. Crop rotation affecte d mycorrhizal fungi, protozoa, and soil peptidase activity, and N fert iliser had a significant effect on mycorrhizal fungi, protozoa, and ce llulose decomposition. As these biological properties are responsive t o agricultural management, they may have potential as bioindicators. T otal bacteria, fungi, and actinomycetes, cellulose-decomposing bacteri a and fungi, soil phosphatase and sulfatase activity, and N mineralisa tion were less affected by these treatments and may therefore have lim ited potential as bioindicators.