Relevance of Organic Matter in Some Chemical and Physical Characteristics of Volcanic Ash-Derived Soils

Abstract

The accumulation of organic matter in volcanic soils may modify their properties and characteristics. Soil complexity makes difficult to assign the relative importance of organic matter in determining soil behavior. If changes in soil properties can be associated with the soil organic carbon (OC) content, a better understanding of the organic matter role may be achieved. A total of 20 samples of uncultivated volcanic soils, located in Central-Southern Chile, classified as Andisols and Ultisols were studied. Properties such as active/free iron oxide ratio (activity ratio), isoelectric point (IEP), cation ORDER REPRINTS exchange capacity (CEC), and potassium-calcium (K-Ca) cation exchange equilibrium were studied in relation to the soil OC content. The activity ratio increases when OC increases showing the inhibitory effect of organic matter in iron oxide crystallization. The IEP increases when OC decreases, this relationship being useful to follow the soil organic matter destruction in sample preparation. The ÁCEC (CEC pH ¼ 8.2 À CEC soil pH ) is directly related with OC, showing that an important fraction of the negative surface charge is the result of ionization of organic matter active groups when pH increases over field value. Selectivity for K over Ca was observed, but decreases when OC content increases and a Ca selectivity may be expected in soils whose OC content is higher than 12.6%.

Characterization, functioning and classification of two volcanic soil profiles under different land uses in Central Mexico

“…Batjes and Sombroek (1997) compared the vertical distribution of the SOC content in different tropical soils and pointed out that contrary to other soils, the SOC content in Andosols is high in the first 15 cm, then decreases by half at a depth of 40 cm, and then does not vary much from 40 to 200 cm depth. The SOC content in the topsoil (0-15 cm) of both profiles of "La Loma" is lower (54 g kg − 1 ) compared to other Andosols: 100 g kg − 1 in the Andosols from Java Island ( Van-Ranst et al, 2002), 140 g kg − 1 in the Andosols from South Ecuador (Buytaert et al, 2002), 95 g kg − 1 in the Chilean volcanic soils (Escudey et al, 2004). Fig.…”

Aluminium stabilization controls organic carbon levels in Chilean volcanic soils

“…Soil C concentration is between 1 and 19%. The mineralogy is dominated by allophanic material, while iron hydroxides and crystalline iron oxides contribute less (Escudey et al, 2004). Soil pH (water) values are between 4.5 in non-limed and 6.7 in limed soils.…”

Sewage Sludge Disposal and Applications: Self-heating and Spontaneous Combustion of Compost Piles - Trace Metals Leaching in Volcanic Soils After Sewage Sludge Disposal

“…These soils are rich in iron oxides and organic matter, and they have pH-dependent variable surface charge and high PO 4 accumulation. However, the soils have poor fertility; at the original acidic pH range of 4.5 to 5.5 they have low capacity for exchangeable cations (CEC) and a strong selectivity for K and Ca over Mg (Escudey et al, 2004b). Phosphorus is strongly fixed by the minerals, and therefore it is not readily available for plant absorption in these soils.…”

“…When soil pH increases the CEC increases, P fixation decreases, and K selectivity is reduced. On the other hand, when the soil's organic matter increases, K selectivity is also reduced (Escudey et al, 2004b). In relation to the impact of biosolids, either in their initial state or as ash, studies in pots and columns have been made on soils derived from volcanic materials.…”