Abstract
SummaryBiochar has the potential to modify soil structure and soil hydraulic properties because of its small particle density, highly porous structure, grain size distribution and surface chemistry. However, knowledge of the long‐term effects of biochar on soil physical properties under field conditions is limited. Using an 8‐year field trial, we investigated the effects of successive additions of high‐dose maize‐cob‐derived biochar (9.0 t ha−1 year−1, HB), low‐dose maize‐cob‐derived biochar (4.5 t ha−1 year−1, LB), straw return (SR) and control (no biochar or straw, CK) on soil aggregate distribution, three‐dimensional (3‐D) pore structure, hydraulic conductivity and water retention in the upper 10 cm of a sandy loam soil from the North China Plain. Results showed that LB and HB treatments increased soil organic C content by 61.0–116.3% relative to CK. Interestingly, biochar amendment did not enhance the proportion of macroaggregates (> 2 and 0.25–2 mm) or aggregate stability, indicating limited positive effects on soil aggregation. The HB treatment decreased soil bulk density, and increased total porosity and macroporosity (> 30 μm). The retention of soil water, including gravitational water (0–33 kPa), capillary water (33–3100 kPa) and hygroscopic water (> 3100 kPa), was improved under HB soil. The HB and LB treatments increased plant‐available water content by 17.8 and 10.1%, respectively, compared with CK. In contrast, SR showed no significant increase in soil porosity and water retention capacity but improved the water stability of macroaggregates. We concluded that biochar used in the coarse‐textured soil enhanced saturated hydraulic conductivity and water‐holding capacity, but did not improve soil aggregation.Highlights Pore structure and hydraulic properties were studied in an 8‐year biochar‐amended sandy loam. HB (high‐dose biochar) increased total soil porosity and CT‐identified macroporosity (> 30 μm). Water retention improved under HB soil. Biochar addition had no effect on the formation of macroaggregates.
Highlights
Biochar has two typical characteristics: it is rich in organic carbon and has a highly porous structure (Lehmann & Joseph, 2015)
The soil organic carbon (SOC) content increased with the rate of biochar application, showing that the SOC content under HB treatment was larger by 34.4% than that of the LB treatment
Biochar addition or straw return had no significant effect on soil ρs (Table 1)
Summary
Biochar has two typical characteristics: it is rich in organic carbon and has a highly porous structure (Lehmann & Joseph, 2015). Previous research has reported positive effects of biochar from different sources on the physical properties of soils of various textures (e.g. sand, loamy sand, sandy loam, silt loam, clay) because of the highly porous structure and large specific surface area of biochar (Basso et al, 2013; Lu et al, 2014; Burrell et al, 2016; Petersen et al, 2016). Biochar from wood and wheat straw are reported to improve the pore system and water retention of coarse textured soils (sandy loam and loamy sand soils) indirectly by increasing root growth and soil organic carbon (SOC) sequestration (Devereaux et al, 2012; Bruun et al, 2014). Many studies found that biochar has negligible or even negative effects on soil physical properties. Peng et al (2011) and Rahman et al (2017)
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