Biogas slurry sustains biochar-mediated crop resilience through enhanced soil pore connectivity

Replacing synthetic nitrogen while sustaining production requires amendments that survive field ageing. Biochar can buffer degraded soils, yet abundant pores do not necessarily form connected transport pathways; whether recycled slurry redirects ageing is unknown. A six-year randomized red-soil trial integrated crop–soil trajectories with recovered-biochar characterization, X-ray CT pore networks, hydraulics, nitrogen pools and microbial functions. With biochar, replacing urea with biogas-slurry nitrogen increased cabbage yield to 55.32 t ha⁻¹ and the sustainable yield index by 0.066 (P = 0.029). Recovered biochar had 70.4% greater surface area and 52.8% more surface nitrogen. Slurry interacted with biochar for pore coordination (P < 0.001) and throat number (P = 0.021), but not pore number (P = 0.192). The combined treatment retained more ammonium and mineral-associated organic nitrogen but less nitrate. Adding coordination to pore-abundance models reduced out-of-sample error by 18.4% for hydraulic conductivity and 14.1% for yield resilience. These observations support a dynamic interface–connectivity mechanism in which slurry-associated reconditioning of aged biochar coincides with topological reorganization of surrounding soil, coupling hydraulic buffering and nitrogen redistribution to crop resilience. Biochar durability therefore depends less on preserving manufactured porosity than on assembling connected soil pathways.