Evaluation of soil biological properties as potential bioindicators of soil health

Abstract

Two long-term field trials in South Australia were used to detect and characterise changes in soil biological properties that were a consequence of different agricultural management. The properties examined were total bacteria, fungi, and actinomycetes; total pseudomonads; cellulolytic bacteria and fungi; mycorrhizal fungi; plant root pathogens (Gaeumannomyces graminis var. tritici, Rhizoctonia solani, Pythium irregulare); bacterial-feeding protozoa; soil mesofauna (collembola and acari); earthworms; microbial biomass; C and N mineralisation; in situ CO2 respiration; cellulose decomposition; and soil enzyme activity (peptidase, phosphatase, sulfatase). The sensitivity of these biological properties was assessed to tillage (no-tillage v. conventional cultivation), 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 management, crop rotation, and N fertilisation significantly (P<0.01) affected C mineralisation and microbial biomass. Tillage with stubble management significantly affected root pathogenic fungi, protozoa, collembola, earthworms, and cellulose decomposition. Crop rotation affected mycorrhizal fungi, protozoa, and soil peptidase activity, and N fertiliser had a significant effect on mycorrhizal fungi, protozoa, and cellulose decomposition. As these biological properties are responsive to agricultural management, they may have potential as bioindicators. Total bacteria, fungi, and actinomycetes, cellulosedecomposing bacteria and fungi, soil phosphatase and sulfatase activity, and N mineralisation were less affected by these treatments and may therefore have limited potential as bioindicators.