Temporary storage of soil organic matter and acid neutralizing capacity during the process of pedogenetic acidification of forest soils in Kinki District, Japan

Abstract

Pedogenetic acidification processes in forest soils derived from sedimentary rocks under mesic and thermic soil temperature regimes (MSTR and TSTR; corresponding to mean annual soil temperatures of 8-15°C and 15-22°C, respectively) in the Kinki District were investigated based on titratable alkalinity and acidity characteristics and soil solution composition. According to statistical analyses of the soil properties, the titratable alkalinity required to acidify soils to pH 3.0 was considered to be derived from reactions occurring at the surface of amorphous Al oxides, while titratable acidity at a pH ranging from 5.5 to 8.3 results from dissociation of acidic functional groups of soil humus and/or deprotonation of oxide surfaces. These reactions were generally more prevalent in MSTR soils. Based on the soil solution composition and titratable alkalinity and acidity in the soil profiles, two processes were postulated for pedogenetic acidification, that is, eluvi-illuviation of inorganic Al followed by subsequent adsorption of dissolved organic carbon (DOC) onto the precipitates of Al hydroxides and comigration of Al and DOC in the form of organomineral complexes. Both processes were conspicuous in MSTR soils and significantly contributed to soil organic matter storage in the subsoil layers. Pedogenetic acidification in forest soils with MSTR was characterized by an accumulation of acidity in the form of amorphous compounds and/or organo-mineral complexes in the B horizon. It seems, to some extent, similar to podzol formation, at least in terms of Al translocation. Amorphous Al hydroxides protect against further acidification through protonation and/or partial monomerization and can, thus, be regarded as a temporary storage of acid neutralizing capacity of the soil, which would be otherwise leached out directly from the soil profile. In contrast, the acid-buffering reactions of TSTR soils seemed to occur, if at all, mostly at or near the soil surface and the contribution of the B-horizon soils was limited.

Describing Phosphorus Sorption Processes on Volcanic Soil in the Presence of Copper or Silver Engineered Nanoparticles

“…On the other hand, the presence of L-ascorbic acid free in soil solution slightly competes with H 2 PO 4 − for available adsorption sites, decreasing H 2 PO 4 − adsorption on T-OM and R-OM soil samples (Figure S8). However, as a consequence of the addition of Cu 0 or Ag 0 ENPs suspensions to soil samples, the pH i values decreased, being less acidic in T-OM as compared to R-OM (Table 4), which was consistent with the buffering capacity of OM [73]. An acid pH can be associated with a decrease in the electrostatic repulsion between H 2 PO 4 − and the negatively charged surface of the organic matter (-COOH, -OH) due to a decrease in the number of deprotonated surface groups [74].…”

Regional trends in the chemical and mineralogical properties of upland soils in humid Asia: With special reference to the WRB classification scheme

“…In solution, the Al 3+ ion behaves as a weak acid through a hydrolytic reaction: that is, Al 3+ + OH − = Al(OH) 2+ (pKa = 5.0), and soils rich in exchangeable Al show a distinct buffer zone against OH − addition during titration (Funakawa et al . 1993, 2008). The strong acidity far below pH 5.0 of some soils must be affected by the presence of a stronger acid(s), that is, H + , although quantitative analysis of exchangeable H + is difficult, and the selectivity coefficient between Al 3+ and H + ions on the permanent negative sites of soils is rarely determined.…”

Proposal for advanced classification of brown forest soils in Japan with reference to the degree of volcanic ash additions

“…However, in other tBFS samples, the Al ox content in the subsurface horizon was not <20 g kg −1 and there was a large lithic fragment, which is not the case in BLS. The Al ox content in some BFS may increase as a result of podzolization without the influence of volcanic ash weathering (Funakawa et al. 2008; Hirai et al.…”