Spatial Variability of the Activity of b– Glucosidases in a Rice Soil in Chile.

Soil enzymes play key biochemical functions in the overall process of organic matter decomposition in the soil system; they interact with physical and chemical properties providing an early indication on the trends of soil quality with changes in agricultural management.  The β – Glucosidase enzymes, which are widely distributed in nature, are active in the final steps of degradation of cellulose into glucose, and are fundamental in the carbon cycle. In the present study, we evaluated the spatial variability of the activity of β – Glucosidase enzymes in a clay soil which has been intensively monocropped with rice.  Soil samples where recollected during the fallow phase, at the beginning of summer, when soils are absolutely dry and cracked.   A 20-ha field was sampled at 10-cm depth, using a systematic non-aligned design with the help of a GPS receiver and sampling software. Sampling intensity was 2.4 samples ha^-1. Soil samples were incubated with THAM at pH 6.5 and extracted by filtration. The activity of β – glucosidase was estimated determining p-nitrophenol released by spectrophotometry.  Enzymatic activity showed a large variability within the field, ranging from 8.6 to 27.4 µg pNP released g^-1 h^-1; although most regions presented low β – Glucosidase activity which is coincident with the low organic matter content of the soil. Relationships between enzymatic activity and selected soil and crop properties are also presented.

Key words: β – Glucosidase, soil quality, soil organic matter, spatial variability.