Comparing the Effects of Biochar and Straw Amendment on Soil Carbon Pools and Bacterial Community Structure in Degraded Soil

The degradation of soil often occurs due to the depletion of organic matter. Both biochar and straw have value as two primary means of remediating soil. In this study, we compared the effects of biochar and straw on soil organic carbon pools and on microbial communities in degraded soil. We added straw (maize) and biochar (maize-derived) to the degraded soil at the ratios of total soil weight (0, 1, 2, or 4%), respectively. Soil samples were collected after 180 days. We determined that upon straw addition, there was an increase in microbial biomass carbon (MBC), dissolved organic carbon (DOC), and easily oxidizable carbon (EOC). Upon biochar addition, there was an increase in soil total organic carbon and recalcitrant organic carbon. Analysis of bacterial community was conducted via 16SrDNA sequencing with an Illumina MiSeq platform and revealed that the relative abundance of Actinobacteria increased, but the Bacteroidetes and Chloroflexi decreased with straw addition. We further found that the addition of straw altered the Shannon and Simpson diversity index values, whereas biochar did not impact soil bacterial diversity. Nonmetric multidimensional scaling and canonical correspondence analyses revealed that bacterial community structure was influenced by both biochar and straw addition. Mantel testing further revealed that this community structure was associated with soil EOC (r = 0.286, P = 0.001), DOC (r = 0.174, P = 0.002), and MBC (r = 0.299, P = 0.002) upon straw treatments. These results suggested that straw can improve soil labile organic carbon pools and soil bacterial communities better than biochar, whereas biochar (via pyrolysis at 550 °C, for 2 h) can improve carbon sequestration better than straw in degraded soil.