Massive carbon addition to an organic-rich Andosol increased the subsoil but not the topsoil carbon stock

摘要: Abstract. Andosols are among the most carbon-rich soils, with an average of 254 Mg ha −1 organic carbon (OC) in upper 100 cm. A current theory proposes limit for OC stocks independent of increasing carbon input, because finite binding capacities soil mineral phase. We tested possible limits already large OC concentrations and (212 g kg first horizon, 301 Mg ha 100 cm). The soils received inputs of 1800 Mg OC ha as sawdust within a time period 20 years. Adjacent without application served controls. We determined total well storage forms matter (OM) five horizons down to 100 cm depth. Storage considered were pyrogenic carbon, OM −3 density little no interaction phase, strongly mineral-bonded forming particles densities between 1.6 2.0 g cm or > 2.0 g cm . two fractions > 1.6 g cm also analysed aluminium-organic matter complexes (Al–OM complexes) imogolite-type phases using ammonium-oxalate–oxalic-acid extraction X-ray diffraction (XRD). Pyrogenic represented only up 5 wt % OC, thus contributed OM. In topsoil horizons, fraction between had 65–86 wt % of bulk was dominated by Al–OM complexes. In deeper the fraction > 2.0 g cm contained 80–97 wt % the bulk soil's total characterized mixture complexes and phases, proportions phases increasing response application, OC stock at 25–50 cm depth increased significantly ( α=0.05 , 1 - β = 0.8 ). increase entirely due However, there no significant increase in results suggest that long-term inputs cannot be taken the obviously OC-saturated but induce downward migration gradually increasing subsurface layers. small additional OC accumulation despite extremely input over 20 years, however, shows long periods high needed promote downward movement deep OC.