Effect of Land Use Change on Soil Properties and Clay Mineralogy of Forest Soils Developed in the Caspian Sea Region of Iran

Abstract

All of the tea plantations in Iran are concentrated in the Caspian Sea region on soils previously developed under deciduous natural forests. This research conducted to study the effect of land use change (from forest to tea) on selected physico-chemical and mineralogical properties of soils under humid climate and mountainous landscape in Northern Iran. Three transects facing west to northwest in both tea plantation and the nearby natural forest were selected. A total of 18 soil profiles formed on different physiographic positions i.e. summit, shoulder and foot slope were studied and morphological features of the soils were described. Soil samples taken from each horizon were analyzed. A two factor completely randomized design was used to take soil samples from surface horizons in each transect. Results showed that after changing forest to tea cultivation pH, cation exchange capacity, clay content and the amount of organic carbon of the soils were decreased at P< 0.01 significance level, but bulk density was increased compared to soils under natural forest. X-ray diffractograms of clay fractions showed that vermiculite, vermiculite–illite mixed layers and hydroxy interlayered clay minerals were the major clay components. Soils under tea cultivation possessed highly developed and more prominent argillic horizons and contained more clay fraction in the lower horizons in all physiographic positions. Keywords: Forest soils, Land use change, Soils of Iran, Tea cultivation.