Aluminum Bonding in Soils: a Unifying Principle in Soil Science

Abstract

The aluminum ion bonds through oxygen to form a variety of functional groups underlying diverse properties of soils. One aluminum-bond functional group provides the cation exchange site of soil layer silicate clays. Pauling's m-rule of acid strength for oxy-acids, (HO) n O m C, applied to the 2:1 layer silicate clay formula of beidellite, considering all structural cations, yields m = 1.6, characteristic of a medium to strong acid strength (on an m-scale: 1 = weak; 2 = strong). The solubility product of A1(OH) 3 , k T of A1(OH.,),, 3 +, and the Pauling k^k;, ratio of 10 5 are applied to calculate concentrations of aluminohydronium monomeric cation species of valence of 3, 2, and 1. These concentrations relate to cation exchange and interlayer aluminum polymerization reactions in soils during chemical weathering. The latter and mineral colloid composition changes are summarized in the generalized bonding equation: Al -O ±^ Al -OH, which provides the ultimate buffer, setting the lower and upper limits of the pH range of soils except in the presence of strong acidforming compounds such as S and FeS 2 . Aluminum bonding is central to soil acidity, through not only the acidic aluminohexahydronium monomeric cations, but also through the weakly acid Al-OH 2 . . . OH pair at edges of polymerized ("precipitated") hydroxy aluminum structures. The aluminum toxicity of soil acidity may involve aluminum bonding and solubility product relations at the soil-root interface and in solutions in soil and sap. Retention by soils of anions such as phosphate and sulfate is closely related to aluminum bonding of these anions (OH replacement). Some aspects of soil aggregate structure involve hydroxy aluminum bonding; loss of aggregates follows intensive cheluviation in the A2 horizon. Aluminum bonding in a real sense supplies a unifying principle for

Aluminium and acidity in Finnish soils

“…The exchange acidity replaced on leaching with unbuffered solution ofa neutral salt is claimed to be mainly due to monomeric trivalent aluminium ions (Coleman et al 1959, Jackson 1963, Chernov 1964, at least in soils low in organic matter (Schwertmann 1961 McLean and Owen 1969). These forms of aluminium are not exchangeable with a neutral salt, but they are proton donors or OH acceptors, which will increase the consumption of base when acid soils are titrated.…”

Case Study of N Deficiency Symptom of Strawberry in the Soil Applied with Sea Deposit Compost

“…기의 pKa 부근은 매우 낮은 pH를 나타내지만 양이온의 함 량이 많아질수록 pH는 높아진다 (Jackson, 1963;Hargrove and Thomas, 1981). 토양 pH가 7.5 이상 높아지면 작물의 생육과 양분흡수가 나빠지게 된다 (Kim et al, 2010 Table 4.…”

B Horizon

“…The acid form represented here is obviously a simplification; however, the hydrogen atoms shown should be considered as protons, which are released whatever the structural form they belong to since, as Jackson (1963) has observed, "fundamentally, all acidity groups depend on proton dissociation, that is exchangeable H þ , but differ only in the acidity strength of the functional groups". The weak-acid groups of the colloidal complex liberate protons into the soil solution; the state of equilibrium between undissociated and dissociated forms can be illustrated by:…”