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Abstract:

Maintaining and improving the quality of soils are vital to provide the food and fiber demands of increasing human population and support the sustainability of the ecosystem services. The aim of this study was to assess the effects of land use change on soil quality and related functions of natural grassland and adjacent cropland which has been used as grassland till 2008. Rotation of forage crops including rye, triticale, barley and second crop silage corn has been applied in the cropland after the conversion from rangeland. Manure (50 ton ha^-1) was applied to all croplands at the beginning of the crop production. A total of 200 surface soil samples (0-20 cm) were collected in June 2012, 68 of which were from cropland and 132 from natural grassland. Soil samples were analyzed for bulk density, aggregate stability, available water content, water-filled pore space, total organic carbon, pH, electrical conductivity (EC), sodium adsorption ratio, plant available phosphorus and extractable potassium concentrations to determine the soil quality index using Soil Management Assessment Framework method. Nutrient cycle, water relations, physical stability and support, filtration and storage, and resilience and resistance sub-functions were examined under the soil quality. Indicators defining the soil functions were determined using expert opinion and principal component analysis (PCA), and weights for each indicator were assigned by using simple additive and weighted additive methods. The aggregate stability included in the data set with the expert opinion was removed from the data set by the PCA approach. Total organic carbon, sodium adsorption ratio and EC were the most frequently used indicators to define soil functions in the study area. Soil quality assessment determined by PCA and expert opinion methods produced significantly different results. The mean sodium adsorption ratio values of cropland and natural grassland were 4.30 and 7.19, and the EC values were 2.48 and 3.66 dS m^-1, respectively. High sodium adsorption ratio decreased the soil quality in both lands. In addition, lower total organic carbon and higher EC values in natural grassland were other causes of low soil quality. Manure addition, crop rotation and irrigation in cropland increased the total organic carbon and decreased the sodium adsorption ratio and EC values compared to the natural grassland. Therefore, contrary to the expectations that converting rangelands into the croplands leads to negative changes in soil functions, conversion of natural grassland to cropland in study area, improved the soil quality. The simplicity and quantitative flexibility of soil management assessment framework allowed to compare and assess the effects of rangeland conversion into cropland.