Effect of tillage and stubble management on chemical and microbiological properties and the development of suppression towards cereal root disease in soils from two sites in NSW, Australia

Abstract

Different tillage and stubble management practices were compared at two sites in New South Wales, Australia, to determine their effect on soil chemical and microbiological properties and the development of suppression towards Gaeumannomyces graminis var. tritici (Ggt) and Rhizoctonia solani. At one site (Harden), the management practices were direct-drilling of crops with stubble retained (DD) and conventional sowing of crops with stubble burnt (CC) for 6 years prior to sampling. At the second site (Cowra), a stubble incorporated (SI) treatment (SI with a single cultivation prior to sowing) was compared with DD and CC treatments and the practices had been in place for 16 years. By comparing the difference in plant growth in γ-irradiated and natural (unsterilised) soil in the presence of added Ggt and Rhizoctonia inoculum, evidence of suppression towards Ggt was observed in soil from both the sites. The suppression was greater in the DD compared to the CC soils. This was associated with higher levels of organic C and total N in the DD compared to the CC soils at Cowra and with higher microbial biomass, CO2 respiration and populations of fungi (including cellulolytic fungi) in the DD compared to the CC soils at both the sites. There was less evidence of suppression towards Rhizoctonia but higher disease levels were obtained from the added Rhizoctonia inoculum in the CC soil compared to the DD soil at both the sites. The results showed that the DD practice augmented a build-up of organic C and microbial biomass in the surface soil and increased its suppressiveness towards two introduced fungal pathogens.