تاثير تغييركاربري اراضي بر ويژگي هاي فيزيكي و عناصر غذائي خاك در منطقه شمال خوزستان

Effects of land-use changes on soil physical characteristics and nutrients in northern Khuzestan

بهمنظور بررسي اثر تغيير كاربري اراضي بر ويژگيهاي فيزيكي و عناصر غذائي خاك اين پژوهش انجام شد. بدين منظور دو كاربري كشت نشده و كشت شده در اراضي كشت و صنعت كارون در منطقه ديمچه شوشتر ر استان خوزستان انتخاب و نمونهها از 7 مزرعه در سه عمق 30 - 0 ، 60 - 30 و 90 - 60 سانتيمتري در سه تكرار تهيه گرديد. درصد شن، رس و سليت، چگالي ظاهري، تخلخل كل، ميانگين وزني قطر خاكدانه، مواد آلي خاك، فسفر قابل جذب، پتاسيم قابل جذب و نسبت كربن به نيتروژن در هر عمق تعيين و نتايج به صورت فاكتوريل و در قالب طرح كاملاً تصادفي بررسي گرديد. نتايج نشان داد كه بيشترين مقدار رس و سيلت در اراضي تحت كشت نيشكر و كمترين آن در اراضي كشت نشده مشاهده شد. با تغييركاربري اراضي مقدار شن از 55 / 22 درصد در اراضي كشت نشده به 67 / 6 درصد در اراضي نيشكر كاهش يافت. چگالي ظاهري و ميانگين وزني قطر خاكدانه براثر تغيير كاربري از كشت نشده به نيشكر به ترتيب 16 و 67 درصد افزايش يافت. همچنين تغييركاربري از كشت نشده به نيشكر سبب افزايش ماده آلي و فسفر قابل جذب و كاهش پتاسيم قابل جذب و نسبت كربن به نيتروژن شد. بهطور كلي نتايج اين پژوهش نشان داد تغييرات ويژگيهاي فيزيكي و عناصر غذائي در خاك سطحي بيشتر از ساير عمقها بود. اين پژوهش نشان داد كه كشت متراكم و آبياري سنگين در دوره طولاني مدت باعث تغيير و تحول ويژگي هاي فيزيكي و مواد آلي خاك ميشود، لذا به منظور مديريت اراضي و حفظ كيفيت خاكهاي بررسي شده پايش ويژگي هاي خاك لازم و ضروري مي باشد

Introduction Land-use changes may influence various natural and ecological processes, including soil nutrients, soil moisture, soil erosion, land productivity and biodiversity. Compact cropping and lack of suitable management approaches in agricultural fields all over the world have affected soil properties in vast areas and led to changes in soil quality. The cultivation of sugarcane in the south of Iran started 60 years ago. The cultivation of sugarcane was mechanized in the southwest of Iran in the late 1950s. Over the past 40 years, the sugarcane yield has been declined from 110 to 50 tons per hectare over the same period. The long-term cultivation period (6 to 7 months), high water consumption (30,000 cubic meters per hectare at 25 to 30 turns irrigation), extensive heavy machinery uses in the planting stage, and sugarcane harvesting may change soil properties. In order to determine how these changes are taking place, it is necessary to examine the land qualitatively and quantitatively to prevent further destruction of this vast God-given source. Due to the fact that few types of research have so far been conducted on the long-term effects of cultivation on the physical and chemical properties of soil, this study aimed to investigate the effect of long-term sugarcane cultivation on some chemical and physical properties of soil in the Karoun Agro-industry Unit in Shoushtar city, Iran. Materials and Methods This research was carried out to investigate the effect of long-term sugarcane cultivation on soil chemical and physical properties in Karoun Agro-industry Unit in Dimcheh with the geographical coordinates Latitude: 32° 02' 60.00 N Longitude: 48° 50' 59.99 E and 68 meters above mean sea level located at 12 kilometers to the west of Shoushtar city in Khuzestan province of Iran. The total area of the land is 45,000 hectares. This area has warm and dry climate conditions. The dominant soils of the area are classified in the large Calcic Haplousteps group. This study was carried out as a factorial experiment based on a complete randomized design with two factors, including fields in seven levels and depth in three levels (0-30, 30-60 and 60-90 cm) and three replications. Soil samples were collected from three depths in six fields with long-term sugarcane cultivation and adjoining uncultivated land. Then, some chemical properties were measured by standard methods: Soil texture by hydrometric method, soil organic matter content by wet oxidation method, the soil sodium bicarbonate extractable phosphorus by Olsen method and available K using 1 N NH4OAc were measured. Also, total porosity and mean weight diameter were calculated based on conventional equations. Statistical analysis of data was performed by SAS 9.2 software, and the comparison of means was made using Duncan's multidomain test at a 1% probability level. Figures were also drawn using Microsoft Excel software. Results and Discussion Results indicated that land-use changes and long-term sugarcane cultivation result in soil chemical properties changes. By land-use changes, the amount of sand decreased from 22.55% in virgin