Improving organic residue quality to reduce CO2 emissions and promote carbon (C) accumulation in a sandy loam soil with low organic matter

Abstract

The objectives of this study were to investigate patterns of changes with decomposition time of carbon (C)-cycling enzyme activities (i.e., invertase, B-glucosidase, phenoloxidase and peroxidase) in response to fresh addition of contrasting chemical composition organic residues into a sandy soil, and the relations of these microbial activities with some soil properties. The experiment was divided into 4 treatments include the following: 1) control (Untreated soil), 2) Soil + Rice straw, 3) Soil + Biochar compost, and 4) Soil + Biochar. The Soil + BC compost treatment showed significantly (P < 0.05) higher invertase activity than the other treatments at the middle to later stages of decomposition (0.17 -0.29 mg GE g^-1 soil DW 3h^-1). Results revealed that the Soil + Rice straw treatment showed significantly (P < 0.05) higher B-glucosidase activity over the other treatment after 7 day (28.9 - 56 μg p-nitrophenol g^-1 soil DW h^-1) which was a testimony to the distinctly high cellulose substrate of this residue, while Soil + Biochar treatment showed higher phenoloxidase activity at all stages of decomposition. At day 21 42 and 63 after incubation, highest activity of phenoloxidase in the Soil + Biochar treatment also showed highest phenoloxidase activity compared to the other treatments (P < 0.05) (0.4 0.88 and 0.67 μmol dicq g^-1 soil DW h^-1, respectively). The positive effect of nitrogen (N) on enzyme activities was seen in the relations of invertase and B-glucosidase at middle to later stages of decomposition. Therefore, there was no negative effect of N on the expression of resistant C compound degrading enzyme activities. We also showed an evident that microorganisms under deprivation of substrate from fresh residue addition for the long term, particularly in a sandy soil may be induced to utilize recalcitrant compounds as C source. In addition, the lowest qCO2 (0.078 mg CO2-C g^-1 microbial biomass C d^-1) under biochar compost-treated soil reflected a high efficiency of C utilization of microbial decomposers. It can be concluded that, among the three residue treatments, biochar compost is the most suitable residue in improving soil organic carbon restoration in a sandy loam soil with low organic matter.