Application of soil quality index in assessing rangeland productivity

Crop growth in natural habitats is the result of the biological function of various factors. Soil is the most influential factor on the yield potential of a habitat that can lead to the soil fertility and yield degradation. This study aimed to determine the relationship between crop yield and soil properties used to calculate the soil quality indicators in the semi-arid rangelands of Shohada-Valley as an example in West Azerbaijan Province The slope aspect with four directions, slope classes with five classes and vegetation layers were overplayed to prepare working units of 1:50,000 scale. Physical, biological and chemical properties of soil samples from 0-30 cm of topsoil were determined through required analysis. Landscape Function Analysis (LFA) was done and yield of dominant species was calculated in maximum flowering time by direct collection method. Effective soil properties on plant production were determined using Principal Component Analysis (PCA) and the mathematical relations between crop yield and soil parameters was computed by stepwise multiple regression. Results showed that mean values of soil landscape index is 0.8, stability index was equal to 76.9, the permeability index was 57.1 and the nutrient index was equal to 69.1 in 28 map units. The average of total production was calculated 1535.24 kg /ha of dry matter. Three components having a latent root above one, explained about 78 percent of the variance using factor analysis,. The outcome variables for evaluating soil quality index, organization index, nutrient cycling index, salinity and bulk density, were determined. A significant correlation of 63% was achieved between soil quality indicators and crop production,. Using soil quality index a coefficient of determination of 64 percent was computed after applying a mathematical crop production model Mean Bias Error of -0.02, error of 8% and the efficiency of the model of 0.66, provide a suitable application for interpretation function of rangelands. Therefore, resulted model is suitable for estimating range production in semi-arid and cold semi-arid steppe habitats.