[Profile distribution of exchangeable calcium and magnesium in an aquic brown soil as affected by land use type]

A comparative study was made on the profile distribution of exchangeable Ca and Mg and Ca/Mg ratio at the depth of 0-150 cm in an aquic brown soil under four land use patterns, i. e., paddy field, maize field, fallow field, and woodland. The results showed that less difference was observed in the soil exchangeable Ca content and storage among different land use patterns. For soil exchangeable Mg, it was significantly higher in woodland than in paddy field, and its storage was in the sequence of woodland > maize field > fallow field > paddy field (P <0.05). The exchangeable Ca/Mg ratio tended to decrease with soil depth, and was significantly lower in paddy field than in other three land use patterns in the soil layers below 40 cm (P <0.05). The preferential retention of Mg in soil ecosystem, soil management practices, and plant characteristics, e. g., biomass cycling rate, biomass above- and below-ground allocation, root distribution, and maximum rooting depth) might play important roles in shaping soil exchangeable Ca and Mg profiles and in reconstructing soil exchangeable Ca and Mg pools.