Soil microbial and chemical indicators of soil heath response to agricultural intensification practices on cracking black clay soils

Abstract

The concept of soil health encompasses the state of the biological, chemical and physical properties of the soil. Possible interactions between these components may determine their response to management practices and their resilience to associated disturbances. The role of soil microorganisms in nutrient and energy fluxes observed in the soil environment, is considered critical in the maintenance of soil health. The sensitivity of soil microorganisms to changes in soil conditions could reflect soil health status and act as indicators of change. In spite of the low organic carbon content and low soil biological activities reported in heavy cracking clay soils (black Vertosol), the response pattern of the soil microbial fraction to different management practices of varying intensities and frequencies of disturbance, could still serve as a sensitive indicator for indicating levels of soil degradation. In the absence of threshold values for a healthy soil, it is critical to evaluate microbial and chemical status in a continuum of land use intensification. This study aimed at evaluating two soil microbial parameters (soil microbial respiration and biomass) and some chemical parameters in different agricultural management practices of varying intensities of disturbance within the same eco-region, and soil type, black Vertosol. Six agricultural management practices were selected, of differing intensities and frequencies of disturbances, in the Warrah sub-catchment, part of the Liverpool Plains Catchment, NSW, Australia. Basal soil microbial respiratory activity and microbial biomass were measured using a Respicond respirometry system. There were significant differences between undisturbed control sites, and all the farm sites along with significant differences between grazing and cropping systems. However, no statistically significant differences were observed between native and introduced pasture systems. Fallow and tillage practices appeared to have a significant effect only in the situation of long fallow, zero tillage that was lower in both microbial biomass and respiration compared with all other treatments. This may be attributed to the low fertilizer use in the system and slow stubble breakdown rates in this system. In most cases, microbial parameters were positively associated with organic carbon and nitrogen levels in the soil.