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The aim of this investigation is to study how adsorbed humus on clay minerals affects kinetics of dissolution of clay mineral by an organic acid in terms of K and Si release. Clay--humus complexes were isolated from soil samples collected from different depths of 2 soil profiles from an Inceptisol of North India under long-term rice--wheat and maize-wheat cropping systems. Clay--humus complexes were subjected to repeat extraction with 100 mg/L of tartaric acid solutions before and after removal of humus with 30% hydrogen peroxide and the resultant release of potassium and silica was measured. Before removal of humus, K release followed Elovich kinetics for the maize wheat cropping system. For the rice--wheat cropping system, except surface soil, which followed Elovich kinetics, other subsurface soils followed the power form of kinetic equations. But when humus was partially removed, K release increased exponentially, therelease rate increasing with time. This indicated that for humus-depleted clay, initial release triggered further release of K. Silica was released at a constant rate. The dissolution reaction was incongruent, i.e. the amount of constituents released in solution was not proportional to their mole fraction present in the mineral. X-ray diffraction analysis showed that micaceous mineral was partially dissolved and vermiculite was completely dissolved when humus was partially removed from clay before extraction. This observation indicates that humus adsorbed on clay plays an important role in preventing clay dissolution by organic acids. Additional keywords: clay, clay humus complex, K, Si, release, tartaric acid., Introduction As soil protects the environment by sequestering carbon and slowing its decomposition, the sequestered carbon in turn protects the soil from dissolution by natural forces. When the rate of [...]

Study on active and labile carbon-pools can serve as a clue for soil organic carbon dynamics on exposure to elevated level of CO2. Therefore, an experimental study was conducted in a Typic Haplustept in sub-tropical semi-arid India with wheat grown in open top chambers at ambient (370μmolmol−1) and elevated (600μmolmol−1) concentrations of atmospheric CO2. Elevated atmospheric CO2 caused increase in yield and carbon uptake by all plant parts, and their preferential partitioning to root. Increases in fresh root weight, volume and length have also been observed. Relative contribution of medium-sized root to total root length increased at the expense of very fine roots at elevated CO2 level. All active carbon-fractions gained due to elevated atmospheric CO2 concentration, and the order followed their relative labilities. All the C-pools have recorded a significant increase over initial status, and are expected to impart short-to-medium-term effect on soil carbon sequestration. [Copyright &y& Elsevier]