Effects of biochar and compost amendments on soil physico-chemical properties and the total community within a temperate agricultural soil

The use of biochar and compost as soil amendments and their comparative effects on microbial activities and related processes were investigated in an apple orchard site at Mountain River in Tasmania, Australia. Biochar derived from Acacia green waste was applied at a rate of 47 ton ha⁻¹ just before planting and has been in situ for 3.5 years. Compost produced by the Luebke system was also applied separately at 10 ton ha⁻¹ as a top dressing one week after planting. Chemical analysis indicated that there was no significant impact on total ions by either biochar or compost additions. However, organic carbon was significantly increased (p = 0.009) by 23% for biochar and 55% for compost treatments. Soil pH decreased in both biochar and compost treatments. Microbial abundance was improved after the addition of biochar, but the effect of compost addition was greater. There were no significant differences across a panel of enzyme activities among treatments. There were slight increases in alkaline phosphatase while fluorescein diacetate activity and hydrolysis activity slightly decreased. The entire community of the soil was assessed using 16S rRNA and 18S rRNA genes amplicon pyrosequencing. Significant differences in bacterial and fungal but not archaeal or other eukaryota community components were observed. These results indicated that biochar and compost carbon amendments can subtly affect the community structure of the orchard soils despite active application of inorganic and organic fertilizers. The overall effects on fundamental activity is largely neutral, however, likely due to the enormous structural resilience and functional redundancy present.