[Effects of combined application of biochar with organic amendments on enzyme activity and microbial metabolic function of carbon sources in infertile red soil].

To improve carbon (C) sequestration and soil fertility of red soil, a two-year (2017 and 2018) field experiment was conducted to investigate the effects of two organic amendments (, corn straw and sheep manure) applied alone or combined with biochar on soil nutrient content, enzyme activities involved in C cycling, and microbial substrate utilization rate in infertile red soil. There were six treatments, including control (non-amendment), corn straw, sheep manure and across biochar treatments (without and with biochar amendment, respectively). The organic amendments and biochar were applied in 2017 and 2018. The results showed that, compared with the control, organic amendments significantly increased soil pH, organic C, total nitrogen, available phosphorus and potassium contents. Compared with straw and manure alone, the biochar co-application with straw or manure significantly increased the contents of soil organic C, available potassium, and available nitrogen, without any significant interactive effects. Application of organic amendments significantly increased the activities of soil β-glucosidase (BG), cellobiohydrolase (CB), β-xylosidase (XYL), and peroxidase (PERO). The combined application of biochar and straw significantly reduced the activity of phenol oxidase (PHOX) by 28.6% and PERO by 22.2% in comparison with straw addition alone, respectively, while the combined application of biochar and manure significantly reduced the activities of α-glucosidase (AG) by 46.1%, BG by 50.9%, XYL by 41.6%, and PERO by 31.3% compared with manure addition alone, respectively. Compared with the control, the application of organic amendments significantly enhanced soil basal respiration and microbial utilization rates of carbohydrates, whereas biochar co-application significantly decreased microbial utilization rates of carbohydrates and carboxylic acids. Microbial C source utilization rates were significantly and positively correlated with the activities of BG and PERO. Thus, biochar co-application with organic amendments can enhance nutrient content and reduce enzymatic and microbial metabolic activities, thereby may facilitate C sequestration and fertility of infertile red soil.