The addition of biochar, sodium silicate, or earthworm is a feasible practice to repair soils disturbed by mining activities, and the reclamation is largely based on the alteration of the diversity and structure of soil bacteria. The objectives of this study were to assess the relative importance of these supplements on soil bacterial community diversity and structure in reclaimed mine areas. A field experiment with soybean was carried out in mining areas to assess the efficiency of nitrogen, phosphorus and potassium (NPK) fertilizers plus those supplements on soil bacterial community structure and diversity by the 16S rRNA sequencing method. Soil chemical properties were analyzed to their effects on the bacterial community structure. The results showed that the application of nitrogen, phosphorus and potassium (NPK) fertilizers significantly increased bacterial diversity, and a further increase was observed in NPK plus biochar, sodium silicate or earthworm addition. Furthermore, a higher number of genera were found in the NPK plus biochar and NPK plus earthworm treatments than that in the control, NPK and NPK plus sodium silicate treatments. The bacterial community was significantly associated with nutrients, such as carbon (C) and nitrogen (N). Moreover, soil organic carbon (SOC) and pH were the most dominant factors in shaping the soil bacterial community structure and diversity. Our data indicate that the addition of earthworms to soil rather than biochar and sodium silicate was the best strategy to mitigate the detrimental effects of mining activities on soil bacterial diversity.
The individual and combined effects of biochar (B) and inorganic fertiliser (F) have all been widely proofed to improve soil fertility and enhance crop growth and yield under irrigation (I) and rain fed conditions. However, the strength of their individual and combined effects on crop productivity has been scarcely reported. In addition, few studies have assessed their individual and co-application effects on economic returns. Therefore, a 2-year field experiment which consisted of factorial combination of irrigation (I) [100% full irrigation (FI), 80% FI and 60% FI], biochar (0 and 20 t/ha) and fertiliser (0 and 300 kg/ha) was conducted. According to the results, irrigation was the dominant factor that influences maize grain yield, followed by inorganic fertiliser and biochar, and they were all significant in their main effects. The strength of interaction effects among, I, F and B on maize grain yield follow the sequence F × I > B × F > B × I. The economic analysis showed that the ternary combination of B, F and I was more economical than the binary combination of B plus I, and F plus I (in that order), when compared with the standalone application of I at maximum production in the field experiment. In addition, combined applications of biochar and fertiliser improved soil nutrients, nutrient uptake in all irrigation treatments, compared to the standalone applications of biochar or fertiliser. Further research is, therefore, recommended for long-term evaluation of the economic viability of integrating biochar with fertiliser under irrigation.
One-pot chemical activation and pyrolysis process was developed for biochar production from red macroalgae residue of Gelidium sesquipedale. The macroalgae residue was activated by various catalysts (KOH, NaOH, H3PO4, and CH4ON2) with the two concentrations (2.5 wt% and 5 wt%) using a pulverization system followed by slow pyrolysis at 500 °C. The activated biochars showed a porous morphology with an increase of water holding capacity compared to the unactivated one. The properties of activated biochar observed by further characterization (i.e., FTIR, SEM, TGA) revealed their feasibility to be used as an adsorbent. The results of adsorption experiment confirmed that adsorption was dependent not only on the surface area but also on the surface charge, and functional groups. The sorption performance of activated biochars (AcBC), in terms of the adsorption of methylene blue, was comparable to commercial activated charcoal (Norit®). NaOH (2.5 wt%)-activated biochar had the removal efficiency of 87% versus 97% for commercial activated charcoal.