Modifications in selected soil attributes as influenced by long-term continuous cropping in a calcareous semiarid environment

Intensified agriculture and irrigation practices over a long-term are an important factor in soil change phenomena that can appear some unwanted effects on soil attributes. To examine this hypothesis, physicochemical properties and clay mineralogy of four major soil types (Typic Haploxerepts, Typic Xerorthents, Typic Calcixerepts, and Fluventic Haploxerepts) under sunflower cultivation over five decades and adjoining virgin lands were investigated in order to monitor changes caused by long-term cropping. The comparison of cultivated soils and virgin lands indicated that cultivation resulted in an increase in clay (3-28 %) and silt (3-25 %) content, along with a decrease in sand content (2-17 %), resulting of the cultivation practices. For most of the examined soils, soil pH and calcium carbonate equivalent were marginally increased as 0.1-0.23 unit and 4-26 mg kg(-1), respectively, following intensive cropping. A relative depletion was manifested in mean value of soil organic carbon (4-18 %), soluble K (47-197 %), exchangeable K (21-34 %), available K (20-34 %), potassium absorption ratio (43-45 %), and exchangeable potassium percentage (26-54 %) due to continuous sunflower cropping. Comparing with the virgin lands, the cultivated soils showed a considerable rise in electrical conductivity (18-122 %), sodium absorption ratio (18-122 %), exchangeable Na (4-48 %), and exchangeable sodium percentage (10-47 %) likely due to the chemistry of the irrigation water used, as well as the chemical interaction between the irrigation water and its receiving soils. Over the five decades of cultivation, some changes in the X-ray diffraction pattern of illite and smectite were observed mainly as result of cropping and K depletion as well as alternating wet-dry periods induced by irrigation practices.