Abstract
The interplay of different mechanisms shaping the biochar impact on soil structure remains relatively unexplored. We investigated the impact of biochar application to two contrasting soils on the stability of soil aggregates under an intensive intermittent leaching regime. A greenhouse experiment was established using PVC columns filled with 500 g soil from an Acrisol or Calcisol amended with three biochar applications (0, 1 and 2% w/w). The columns were watered weekly (100 mL) during two leaching cycles (each lasting 10 weeks). The amount of leached base cations, the stability of 1–2 mm aggregates fraction and soil chemical properties were determined. Biochar enhanced the leaching of the studied cations, but the content of base cations and effective cation exchange capacity remained higher in the biochar-amended Acrisol when compared to control soil. In both soils, biochar reduced the amount of water-stable aggregates, which seemed to be attributed to the increase of K in the exchange complex in the Acrisol while no significant correlation was detected between aggregation in Calcisol and other variables. The negative impact of biochar on soil aggregation is likely linked to higher sensitivity of biochar-amended soils to aggregate disruption under changing moisture conditions caused by frequent and intensive leaching events. These results highlight the gaps in our understanding of biochar impact on soil aggregation, which have implications for soil erodibility or restoration of degraded lands under changing climate.
Highlights
The capacity of biochar to reduce soil bulk density and increase soil porosity has been widely accepted in a wide range of soils [1]
The leaching of Na was unaffected by biochar addition in Acrisol; in Calcisol, Na concentration in the leachate was significantly higher in B2 than in B0 during the first leaching cycle, while in the second cycle, the Na losses were below the detection limit (Figure 1 and Figure S1)
The content of soil aggregates and the amount of water-stable aggregates (WSA) per kg of soil decreased in all treatments from the initial WSA contents, which indicates that biochar application promoted higher aggregate disruption rather than reduced WSA formation during the leaching experiment in comparison to laboratory incubation
Summary
The capacity of biochar to reduce soil bulk density and increase soil porosity has been widely accepted in a wide range of soils [1]. Many authors have reported enhanced formation of water-stable aggregates (WSA) after biochar application to soil [1]. The improvement of soil structure has been linked to increased microbial activity and aggregate stabilization by polysaccharides from microbial metabolism [2,3], and to the adsorption of organic matter onto biochar surface [4]. Owing to its high carbon (C) content, biochar application to soil is a powerful way to sequester organic C, but could be a promising strategy to improve soil structure, which is an essential step in preventing soil erosion and reducing nutrient losses. Biochar had a lower effect on soil aggregation
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