The effects of biochar on soil nutrients status,microbial activity and carbon sequestration potential in two calcareous soils

Biochar as an organic amendment improves soil attributes,with a potentially significant effect on soil chemical fertility and quality.The main objective of this study was to quantify the effect of biochar addition on nutrients,carbon sequestra-tion and microbial activity and understand the mechanisms of controlling biochar effects in calcareous soils.Maize residue biochars produced at 200,400 and 600℃ were added at 5 and 10 g kg^(−1)rates to sandy loam and clayey texture calcareous soils.The soil properties measured were pH and electrical conductivity(EC),plant-available potassium(K)and available phosphorus(P),total nitrogen(TN),C sequestration;and the fluorescein diacetate(FDA)hydrolysis activity.Addition of raw material and biochars increased pH(0.15-0.46 units),EC(0.14-0.38 dS m^(−1)),TN(63-120%),K(12-41%)and FDA activity(27-280%),but tended to decrease plant-available P(23-86%).Increasing pyrolysis temperature increased soil C pool index(CPI),but decreased the FDA and the changes depended largely upon the application rate and soil texture.The positive effects of biochar addition and its pyrolysis temperature on soil C sequestration potential were more pronounced at high than low application rate and in sandy loam than clayey soils.Nevertheless,the effect of biochar addition and pyrolysis temperature on the FDA activity was higher at high than low application rates,but lower in sandy loam than clayey soils.Although biochar application may successfully improve soil processes and attributes and have a high potential for C seques-tration,its effects are controlled by soil texture,pyrolysis temperature and application rate.

Short-term effects of maize residue biochar on kinetic and thermodynamic parameters of soil β-glucosidase

Soil β-glucosidase (BG), the rate-limiting enzyme in the final step of cellulose hydrolysis, plays a key role in microbial metabolism, carbon (C) cycling and sequestration in terrestrial ecosystems. Biochar application is known to affect soil BG activity;however, most of the biochar studies have focused on the potential activity of BG, and it is not clear how biochar influences the kinetic and thermodynamic behavior of BG in the soil. The objective of this study was to investigate the effect of maize residue biochar on soil BG kinetic and thermodynamic parameters. Soil BG kinetic (V_(max) and K_(m)) and ther-modynamic (E_(a), ΔH_(a) and Q_(10)) parameters were determined within soils (clayey and sandy loam soils) amended with either maize residue (as positive control) or its biochar (600℃) at 0.5 and 1.0% ratios (w/w), and the mixtures were incubated for 90 days. BG showed an increase in potential enzymatic activity (81%), enzyme concentration (higher V_(max) value) (25%) and substrate affinity (lower K_(m) value) (32%) in the biochar-amended sandy loam soil only at high addition rates compared with the control, and an increase by about 86% of the catalytic efficiency (V_(max)/K_(m)). In the clayey soil, biochar addition decreased potential BG activity (by 10-29%), increased the V_(max) value (by 20-25%) and had no impact on enzyme-substrate binding affinity, but still increased the catalytic efficiency by 47-72%. Adsorption of soil BG by biochar particles did not affect the catalytic efficiency in the soil. Generally, application of maize residue biochar to the soil decreased the E_(a), ΔH_(a) and Q_(10) values of BG compared with the negative controls at both biochar rates in the light-textured soil and only at low biochar rate in heavy-textured soil. The direction and magnitude of BG responses (activity, kinetics, and thermodynamics) to biochar were more related to the soil characteristics. Biochar would increase soil BG thermal stability and decrease its sensitivity to increasing temperature and global warming.