The Effect of Biochar Amendment and Slurry Application on Soil Aggregation and Organic Carbon Distribution

Abstract

【Background and objective】 Biogas slurry and biochar have been increasingly used to amend soils for different purposes ranging from as soil conditioner to fertilizer. While their influence on soil properties has been well documented, their impact on soil aggregation and the consequence for soil organic distribution was poorly understood. The purpose of this paper is to fill this knowledge gap. 【Method】 The experiment was conducted in the field with no biochar amendment taken as the control (CK). For each biochar amendment (B), there were three slurry (originated from pig manure) applications at volumetric ratios (water∶slurry): 1∶6 (BS1), 1∶4 (BS2) and 1∶2 (BS3), respectively. Soil samples were taken from each treatment at the end of the experiment, and the proportions of aggregates of different sizes in the range of >5 mm, 2~5, 1~2, 0.25~1 mm and 0.25 mm aggregates significantly by 13.0%～36.3%, compared with the CK. The mean weight diameter (MWD) and geometric diameter (GMD) of the aggregates in all treatments were both higher than that in the CK, increasing by 9.8%～39.3% (MWD) and 10.0%～37.5% (GMD), respectively. Both MWD and GMD peaked when the slurry application was 1∶4. All treatments also increased soil organic carbon in aggregates of different sizes significantly, beneficial to soil quality. Significant positive correlations were found among organic carbon content in different aggregates, macro-aggregates (>0.25 mm), MWD and GMD (P<0.01). The treatments reduced soil bulk density significantly, with the highest decrease being 6.7% in B+BS3. All these showed that applying biochar and pig manure biogas slurry to soil has a significantly positive effect on soil aggregation, improving soil structure and carbon sequestration. 【Conclusion】 Biochar amendment and biogas slurry irrigation improved soil quality. For all treatments we compared, the optimal application of biochar and the slurry was 12 t/hm2 and 1∶4, respectively.

Keywords

• biochar and biogas slurry
• mean weight diameter of soil aggregate
• organic carbon
• resource utilization