Impacts of continuous biochar application on major carbon fractions in soil profile of North China Plain’s cropland: In comparison with straw incorporation

Abstract

Although the increase of soil organic carbon (SOC) in biochar-amended soil has been well documented, there is a lack of understating on the responses of soil inorganic carbon (SIC) to biochar application in soil profile. Here, we conducted a field study to investigate the effects of 10-year application of biochar at 4.5 Mg ha−1 yr−1 (B4.5) and 9.0 Mg ha−1 yr−1 (B9.0), and straw return (SR) of 15 Mg ha−1 yr−1 on SOC and SIC and their dissolved fractions. Our results showed significant difference in SOC content over 0–20 cm, with an order of B9.0 (8.46 g kg−1) > B4.5 (7.58 g kg−1) > SR (6.81 g kg−1) > control (5.26 g kg−1). However, SIC content was significantly lower under biochar (1.0–2.0 g kg−1) and control (1.0–2.0 g kg−1) than straw incorporation (3.2–3.7 g kg−1) over 0–40 cm. On average, DOC:SOC ratio (an index of SOC desorption) was significantly lower under biochar (~2.0%) and SR (2.6%) treatments than under control (3.1%), implying that both biochar and straw amendments can enhance SOC stability. Over the ten years, 62–81% of biochar-C was converted to SOC in the 0–100 cm layer, which was significantly higher than that (21%) of straw-C. Our estimation suggested that total carbon loss rate was 51–53% under biochar amendment and 70% with straw incorporation. This study highlights that biochar application has great potential for carbon sequestration in cropland of north China.