The influence of land use and fallow period on the properties of two calcareous soils in the humid tropics of southern Mexico

Calcareous soils are common in the humid tropics of Mexico, but little is known about their productivity and resistance to changes in land use. The influence of land use and duration of fallow on physical and chemical properties were investigated in (a) a loamy Rendzina (at Site A) rich in organic matter and limited in depth by calcareous gravel, and (b) a deeper Calcaric Phaeozem (at Site B) with a more clayey texture throughout. Plots at different successional stages within farmers' shifting cultivation systems were selected on both soils: cropland/young fallow (zero years fallow length), shrub-fallow and tree-fallow at Site A, and cropland/young fallow and forest at Site B. Changes in soil properties suggested a process of recovery with fallow length, in which organic matter, total N and CEC increased with time. The increase in organic matter was remarkably large, on average 0.5-0.6% per year. The Rendzina contained more organic matter than the Calcaric Phaeozem, probably because of its greater carbonate content, which is presumed to protect organic matter against decomposition. The differences in soil properties were mostly greater over time than between treatments.