Abstract
This paper focuses on the tensile strength (Q) and porosity of Dystric Cambisol cylinders with and without biochars (0.1% or 5% dose) obtained from wood waste (BC1) and sunflower husks (BC2). The experiments were performed on air-dried and wetted artificial aggregates remolded from unfractionated soil and its selected fractions (1–0.25, 0.25–0.1, 0.1–0.05, and <0.05 mm). The obtained results indicated that the biochar addition reduced the tensile strength of all examined samples, regardless of the type of biomass used in pyrolysis. This effect was more significant with the larger biochar dose of 5%. When cylinders formed from a wetted 1–0.25 mm fraction with 5% BC2, the Q reduction equaled as much as 0.048 MPa. The noted decrease in tensile strength was mainly associated with the formation of macropores in the cylinders (of maximum radii: 4.77 µm BC1 and 5.78 μm BC2). The highest tensile strength was observed in the air-dried samples formed from the largest silica-rich fraction (1–0.25 mm) without biochar (0.078 MPa for the air-dried cylinders and 0.066 MPa for the wetted ones). The higher Q parameter for the air-dried remolded soil aggregates was probably related to the dehydration of soil gels and the thermal transformation of iron and alumina oxides during drying.
Highlights
Aggregation is a significant process in soil—it determines a soil’s structure, stability, and air–water properties
In response to the discrepancies in literature reports about the effect of biochar on soil aggregate tensile strength, this paper focuses on the tensile strength of Dystric Cambisol cylinders with and without biochars obtained from wood waste and sunflower husks
Due to the higher content of large macropores in the sunflower husk biochar, the cylinders with this material contained macropores of larger sizes. This indicated that the biochars obtained from different biomasses affected the porosity of Dystric Cambisol cylinders to varying degrees
Summary
Aggregation is a significant process in soil—it determines a soil’s structure, stability, and air–water properties. Horel et al [24] examined the physical properties of silt loam soil after the addition of biochar They studied natural aggregates and used the following amounts of biochar: 0.5%, 2.5%, and 5.0%. Ouyang et al [28] studied silty clay and sandy loam soil aggregation with and without biochar (2%) obtained from dairy manure They examined natural aggregates and stated that the selected carbon-rich material enhanced aggregate formation. The changes in artificial aggregate tensile strength observed with biochar were combined with the pore size distribution in the samples, determined using mercury porosimetry. Such an interpretation of the results is rare in the existing literature. The authors hypothesize that the addition of biochar decreases aggregate tensile strength because large pores form in soil aggregates when biochar is present
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