CHRONOSEQUENCE IN ALMAR RIVER FLUVIAL-TERRACE SOIL

The aim of this work was to analyze how soils formed fundamentally fro m the erosion of granites evolve under a subhumid Mediterranean climat e as a function of age. Their evolution was evaluated by means of the changes in components and properties, as well as the use of developmen tal indices. The soils are Xerorthents (Holocene), Haploxeralfs (Upper Pleistocene), and Palexeralfs (Middle Pleistocene). The properties ha ve been subject to several trends: (i) some properties increase with r egularity throughout the chronosequence (available water and coefficie nt of linear extensibility [COLE] of the Bt horizons) (ii) other prope rties increase strongly only during the first phases, while some conti nue to increase with age but only moderately (Ap horizon water retenti on and cation-exchange capacity, Bt horizon dithionite-citrate-extract able Fe, solum thickness, clay accumulation, quartz content, and quart z/feldspar ratio), whereas other Middle Pleistocene age soil propertie s cease to increase (the Ap horizon silt and available water, and Bt h orizon water retention and cation-exchange capacity; (iii) others decr ease with age, with pronounced decreases during the first phases (Ap a nd Bt horizon feldspar content and sand content and Bt horizon bulk de nsity); and (iv) some properties are not age related (the Ap horizon b ase saturation and N content and the Bt horizon silt content). The hor izon development indices and the soil development indices indicate goo d relationships with age. In most cases the rate of increase declines strongly for the oldest soils. In the great majority of cases, the pro perties and development indices continue to evolve through the chronos equence without reaching a steady state.