Effects of Land Use Changes on Some Soil Chemical Properties in Khoy, West Azerbaijan Province

Intensified agriculture over a long-term is an important factor in soil change phenomena that can cause some unwanted effects on soil properties. To examine this hypothesis, chemical properties of the soils under sunflower cultivation over five decades and adjoining virgin lands were investigated in order to monitor changes caused by long-term cropping. The studied soils are influenced by continuous sunflower cultivation along with flooding irrigation and using chemical fertilizers for over five decades This research was undertaken at Khoy area (38o 10′ to 38o 40′ N latitude and 44o 15′ to 45o 10′ E latitude) as the northern part of western-Azarbaijan province in the north-west Iran. The Khoy area is characterized by a semi-arid climate (mean annual rainfall of 300 mm) linked with soil moisture and temperature regimes of xeric and mesic, respectively. Agriculturally, the studied area is cropped continuously by sunflower-wheat or barley rotations for over five decades and has received irrigation water from rainfall, groundwater, or seasonal river water. Forty soil surface samples (0-30 cm) belonging to 10 soil series from the cultivated soils and the adjoining uncultivated soils were samplied and analyzed for the different chemical properties. In each soil serie, the samples (cultivated soil and adjacent virgin land) were selected in similar slope, aspect, drainage condition, and parent materials. Soil analyses were involved soil pH and electrical conductivity (EC), soil organic carbon (SOC), Calcium carbonate equivalent (CCE), cation exchange capacity (CEC), total N, soluble K, exchangeable K, and available K. Potassium absorption ration (PAR) was calculated by the concentration of solution K, Ca, Mg and exchangeable potassium percentage (EPP) was calculated by exchangeable Na and CEC values This study illustrate that long-term continuous sunflower cropping had considerable effects on some soil chemical attributes. Over five decades of cultivation, a depletion face was observed in soil organic carbon, CCE, and some K forms (solution, exchangeable, available K) for most of the studied soils. In contrast, an enrichment aspect was occurred in the values of EC. The results showed that soil pH and calcium carbonate equivalent were increased by 0.09 – 0.39 units and 16 – 26 g.kg-1, respectively, in most of the examined soils after intensive agricultural practice. Increase in the CCE value may be caused by tillage operation because of the calcareous parent material is tilled periodically by farmers to cultivate a certain depth of soil in the studied soils. Compared to the uncultivated soils, the cultivated soils showed a relative enrichment in electrical conductivity (20 – 80%) which could be attributed to the chemistry of the irrigation water used and the interaction between the irrigation water and its receiving soils. A slight decline was observed in soil CEC values (1 – 9%) probably due to destruction of soil organic matter. There was a decreasing pattern in the content of soil organic carbon with cultivation ranging 17 to 39% which could be associated with the environmental conditions and management practices, i.e. (a) in the cultivated soils much of plant residues is removed or burned after harvest, (b) the present of livestock after harvest which can result in a substantial loss of SOC, (c) breaks up, decomposition, and mineralization of organic matter is accelerated by tillage practices, (d) the relatively high temperature in the cultivated soils compared to the uncultivated soils which might enhance oxidation of organic matter and destroying of organic C. A relative depletion was observed in the mean value of soluble K (10 – 330%), exchangeable K (25 -40%), available K (16 – 41%), potassium absorption ratio (16 – 61%), and exchangeable potassium percentage (26 – 40%) following continuous sunflower cropping mainly as removal of most sunflower residues after harvest and high uptake of K by sunflower as a high –K- requiring crop. In spite of the fact that exchangeable and available K declined by cropping for most of the studied soils, the soils were grouped as optimal to high category based on two the K forms. This means that intensive rotation cropping not be able to deplete soil exchangeable and available K below a certain level manly due to the presence of the high levels of K-bearing minerals. Overall, the chemical properties of different soil series reflected different responses to (both increasing and decreasing pattern) long-term sunflower cultivation. Organic carbon, soluble and exchangeable K along with EC was known to be the most sensitive indicators following long-term continuous sunflower cropping and irrigation practices. In this cause, it seems hat monitoring the chemical characteristics of both the irrigation water and the soil must be considered in order to establish the water –soil-plant management strategies that will help to prevent environmental degradation and to maintain the overall heath of the studied soils.