Carbon mineralization in subtropical dryland soil amended with different biochar sources

Subtropical soils of Pakistan under dryland agriculture are deficient in organic matter (< 0.5%) due to the high rate of organic matter decomposition in these soils. Biochar materials can improve carbon stock and storage in these soils due to their recalcitrant organic C and protective effect on native soil carbon mineralization. A laboratory incubation experiment was conducted to study the mineralization of biochars prepared from different organic wastes after soil application and to evaluate the effect of biochars on organic C fractions in soil. A subtropical sandy loam soil (Udic Haplustalf) was collected from the University Research Farm, brought to the laboratory, processed, and pre-incubated. Five hundred grams of the soil was added to incubation jars, separately, and the following treatments were applied: (i) Control (no biochar), (ii) biochar-1 (sugarcane bagasse biochar), (iii) biochar-2 (poultry litter biochar), and (iv) biochar-3 (wheat straw biochar). Each biochar was applied at two application rates, i.e., 0.5% and 1.0% w/w maintaining three replications; moisture contents were adjusted at 50% of soil WHC, and the jars were incubated at 25 °C for 90 days. Maximum cumulative CO2-C evolution (∑CO2-C) was recorded from the soil amended with biochar-2, followed by biochar-3 and biochar-1 at 1% application rate. In the start of incubation, dehydrogenase activity (DHA) and microbial biomass C were highest in Biochar-2 amended soil whereas, at later stages of incubation, biochar-3 amended soil had highest microbial activity as compared to other two biochars. Particulate organic C and total organic C remained highest in biochar-3 amended soil throughout the incubation as compared to other two biochars. It is concluded that biochar-2 had more labile organic C with a faster rate of mineralization, while the biochar-3 had more recalcitrant organic C and thus was more effective in C storage as compared to the other two biochars.