Short-Term Impact of Tillage and Residue Management on the Microbial Dynamics Influencing the Soil Carbon of Dryland Farming System.

Short-term impact of tillage and residue management on the microbial dynamics influencing the soil carbon of Dryland farming system

Promil Mehra¹, Nanthi Bolan^1,2,3, Risha Gupta⁴, Jack Desbiolles⁵

¹ Centre for Environmental Risk Assessment and Remediation, University of South Australia, Mawson Lakes,South Australia 5095, Australia, ²Global Centre for Environmental Risk Assessment, University of New Castle, NSW, Australia, ³Cooperative Research Centre for Contamination Assessment and Remediation of the Environment, PO Box 486, Salisbury, South Australia 5106, Australia⁴Phonomics and Bioinformatics Research Centre, School of Information and Mathematical SciencesUniversity of South Australia, Mawson Lakes, South Australia 5095, Australia, ⁵ Barbara Hardy Institute, University of South Australia, Mawson Lakes, South Australia 5095, Australia

Agricultural practices affect the physical and chemical characteristics of the soil, which in turn influences the soil microorganisms as a function of the soil biological environment. However, there is little knowledge available on the interactions between agricultural management practices, based on the short term (2 year), on the soil biochemical properties to find out the effective contribution of different microorganisms (fungal, bacteria) that increases the soil microbial activity under a dryland faring system. A study was conducted to understand the impact of microbial dynamics on the soil organic carbon (SOC), under no-tillage (NT) and conventional tillage (CT) systems with 0, 2.5 and 5 t/ha residue mulching levels. Our results demonstrated from the total 288 hours of incubation indicate that cumulative CO₂emitted from the mineralizable carbon under NT from 0-10 cm depth was significantly lower (P<0.05) by percent decrease (22% to 39%) across mulching levels than C system. Further, it was found that dehydrogenase enzyme activity (DHA) and microbial biomass carbon (MBC) were both significantly higher (P<0.05) under NT, namely 46%, 49.6%, 74.7% (DHA) and 28%, 34.5%, 39% (MBC) across the mulching levels (0, 2.5, 5t/ha) respectively. In general, it was found that the enzyme activity and MBC decreased with the increase in depth (0-10, 10-20 and 20-30 cm) with the increase in mulching rate (0, 2.5 and 5 t/ha) in both the tillage systems. However, the microbial activity of different microorganisms like fungal and bacterial activities were determined by substrate-induced inhibition respiration using antibiotics like cycloheximide (16mg/gm of soil) and streptomycin sulphate (14 mg/gm of soil), by trapping the CO₂ using an alkali (0.5M NaOH) solution. Through platting technique method it was found that  bacterial activity were dominated by fungal activity, where during the first 24hrs of incubation fungal activity were higher under CT, and later it was dominated by bacterial activity under NT system. In conclusion, it is expected that changes in the relative abundance and activity of different microorganisms (bacteria and fungi) under different tillage systems can significantly affect the C cycling and storage due to its unique structures and differential interactions with the soil physical properties.