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Transient Effects of Biochar and Drainage Systems on Soil Granulometry, Bulk Density, and Porosity in Clay Loam Anthrosols Under Monsoon Climate

A. Brikmans,Olga Nesterova,A. Egorin,M. Bovsun,V. Semal,N. Sakara

Published 2025 in Soil Systems

ABSTRACT

Heavy-textured soils in monsoon-affected regions face challenges related to waterlogging and structural degradation, yet the long-term efficacy of biochar as a physical soil amendment under such conditions remains inadequately understood. This two-year field study (2018–2019) therefore evaluated the transient impacts of birch-derived biochar (360–380 °C pyrolysis; 0, 1, 3 kg/m2), subsurface drainage systems, and fertilizer regimes on key physical properties of Endoargic Anthrosols (clay loam) in coastal Primorsky Krai, Russia. Granulometric composition remained stable (silt loam: sand 42–48%, silt 38–44%, clay 12–16%), though drainage significantly increased the silt fraction by >7.5% (p < 0.05). Biochar induced short-term reductions in bulk density (ρb; max −12% at 3 kg/m2, 2018) and aggregate density (ρa; max −9.3%, 2018), but these effects dissipated by 2019 due to tillage redistribution and monsoonal fragmentation, as verified by SEM. Total porosity fluctuated seasonally (0.50–0.65 cm3/cm3), peaking post-tillage but declining under monsoon saturation, with no significant sustained biochar contribution. Crucially, intra-aggregate pore architecture (2–50 nm) resisted amendment-induced changes; N2 adsorption showed treatment-invariant mesopore dominance (65–75% volume; mean pore diameter 17–21 nm), attributable to biochar’s physical exclusion (>1 µm particles from sub-0.5 µm pores) and inert fragmentation. Drainage dominated structural dynamics, modulating pore volume seasonally (−15% in 2018; +18% in 2019), while organic fertilizer enhanced porosity through polysaccharide-stabilized microaggregation (+22%, 2019). We conclude that biochar’s physical benefits in clay loams under monsoon climates are transient and dose-dependent, operating primarily through inter-aggregate macroporosity rather than intra-aggregate modification, necessitating reapplication for sustained improvements.

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