Soil carbon and nitrogen pools and microbial properties in a 6-year-old slash pine plantation of subtropical Australia: impacts of harvest residue management

Harvest residue management can affect the dynamics of soil carbon (C) and nutrient pools and associated soil microbial processes. A field experiment was conducted to investigate the impacts of harvest residue management practices on soil C and nitrogen (N) pools in a slash pine plantation grown on a sandy soil of subtropical Australia. Results showed that harvest residue retention significantly enhanced accumulation of soil total C and N compared with residue removal. The NH4+-N was the predominant form of soil mineral N, and there were no significant impacts of residue management practices on concentrations of soil NH4+-N measured at the time of sampling. Concentrations of water-soluble and hot water extractable organic C and total N tended to be higher in soil with residue retention compared with residue removal, but this trend was only significant for hot water extractable organic C (HWEOC) in surface soil (0-10 cm). Residue retention also tended to increase soil microbial biomass C and N, but did not significantly affect soil respiration and metabolic quotient (qCO2). Direct C and N inputs into soil from the residue layer and moderation of the variation of soil moisture and temperature over the seasons by harvest residue cover might have contributed to the accumulation of soil C and N and microbial biomass with the residue retention treatments. The lack of statistically significant differences in some of soil microbial properties (e.g. microbial biomass C, respiration, etc.) might have been related to a large spatial variability among replicate plots at the experimental site.