Abstract
Biochar is considered to have potential use in carbon (C) sequestration and has been widely used in soil amendment. Humic substances (HSs), assigned as the stable organic C, have obvious agronomic benefits. However, the response mechanisms of these carbonaceous substances to biochar are unclear in biochar-amended soils. In a two-year experiment, the δ13C technique was employed to trace the fate of the biochar-derived C in HSs and evaluate the effects of four treatments, including no biochar control (CK) and biochar addition at dosages of 6 t ha−1 (BC6), 12 t ha−1 (BC12), and 24 t ha−1 soil (BC24), on soil organic carbon (SOC) and HSs. Compared to CK, biochar application significantly improved total SOC contents and the C pool index, whereas the C labile index declined. Humic acid (HA) and humin were distinctly enhanced in bulk soil. Moreover, the aliphaticity was intensified in the chemical composition of HA. In particular, native HA contents substantially increased by 16.30–55.95%. Biochar-applied C of 4.08–6.43% was finitely involved in HA formation over the two years, which resulted in a genetic relationship between soil HA and biochar to some extent. The low dosages of biochar at 6 t ha−1, 12 t ha−1 and 24 t ha−1 did not obviously affect native SOC contents. Moreover, BC24 had less of an effect on HA formation compared to BC6 and BC12, but had the highest SOC. These results demonstrate that biochar application can improve SOC stocks, reduce C instability and promote HSs formation, and they suggest that determining and keeping an optimum dosage of biochar application can represent an effective strategy (i.e., not only sequestrate C, but also improve soil quality), which is beneficial to sustainability in the ecological environment and agriculture.
Highlights
IntroductionThe return of agricultural straw to the soil is still a predominant and effective practice for improving soil quality and recycling nutrients
A pot experiment was conducted in November 2015 by mixing different dosages of biochar derived from maize straw (Zea mays L., C4 plant) into a soil historically planted with soybean (Glycine max (L.) Merr., C3 plant) for more than 12 years
Biochar application significantly enhanced the contents of relatively stable Humic acid (HA) and Hu and aliphaticity of HA as well
Summary
The return of agricultural straw to the soil is still a predominant and effective practice for improving soil quality and recycling nutrients. It can increase carbon (C) input and nutrient element supply, decrease mineral fertilizer input, improve crop yield, and mitigate potential air pollution from in situ straw burning [1]. Biochar is defined as a carbon-rich solid product derived from agro-forestry biomass waste [7] such as energy crops (miscanthus, willow, etc.), forest waste Significant greenhouse gas emissions, especially CO2 , can occur under circumstances where straw application increases the C inputs and C stocks [2,3,4,5], resulting in a higher global warming potential than conventional fertilization systems [6].
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