Land Suitability Evaluation and Inherent Soil Fertility Quality for Rice Cultivation in Paddy Fields of Shaft and Fouman Counties

Many methods have been developed since the formulation of the FAO framework for land evaluation and several of them still remain in widespread use. The objective of this research was to determine land suitability (using FAO method) and inherent soil fertility quality (using fuzzy membership function) for rice crop in paddy fields of Fouman and Shaft counties in northern Iran. Based on results obtained from FAO method, after climate factor (the limitation of the ratio of sunshine hours to day length i.e. n/N, and mean temperature in the growing cycle[b1] ) which was the major limiting factor for irrigated rice cultivation in the study area, drainage was the most soil-limiting factor. Based on inherent soil fertility quality, thickness of the plow layer, which affected root penetration and available soil volume for nutrients, was the most important limiting factor. Based on FAO method SQRI, 92.4% of the study area were marginal and 7.6% were in moderate suitability class, however, according to CLI, all of studied lands were in moderate suitability class. Also, based on inherent soil fertility quality, most of the study area were in suitable (38%) and highly suitable (27%) classes. Correlation of the FAO (SQRI and CLI) and soil fertility quality calculated indexes showed that the indexes were significantly correlated with each other (r=0.7, p