SEASONAL FLUCTUATIONS AND CROP INFLUENCE ON MICROBIOTA AND ENZYME-ACTIVITY IN FULLY-DEVELOPED SOILS OF CENTRAL SPAIN

Soil biological activity in the Mediterranean region is subject to suc cession of favorable and unfavorable periods as a consequence of clima tic conditions. In fully developed soils (Aquic Haploxerult and Aquult ic Haploxeralf) of central Spain and under natural vegetation (evergre en oak) and different degrees of human intervention on vegetal cover ( brushwood and cereal crop), the seasonal dynamic of microflora systema tic groups and enzyme activities was studied. Total microflora, actino mycetes, fungi, and algae tend to decrease according to the sequence: evergreen oak > brushwood > cereal, spring and autumn being the favora ble seasons. Most of enzyme activities show the same sequence of varia tion as the soil microflora groups: from natural vegetation to croplan d. The highest values appear during spring, while the lowest are given in autumn or winter. Factorial analysis establishes a clear differenc e between natural vegetation, brushwood, and cereal (spatial variation ). There is a seasonal grouping subject to that which tends to group t he spring and autumn samples on one hand and the summer and winter on the other (seasonal variation). Results show a significant reduction o f soil microflora populations and catalytic capacity in cropland, sinc e the brushwood maintains patterns that are closest to that of natural vegetation. On the other hand, the favorable seasons have a different meaning, from our point of view. Spring would correspond to a phase i n which the edaphic metabolism produces a significant release of nutri ents (there is a greater intensity of enzymatic processes), while autu mn would correspond to a phase in which an opportunistic exploitation of resources (proliferation of r-strategy organisms) predominates.