Comparison of two fuzzy methods to determine the optimum soil depth in land suitability evaluation for wheat

Land suitability evaluation as part of a sustainable agricultural ýsystem, leads land utilization to a direction, which can preserve land quality in a desirable ýlevel while ensuring the highest income. In the traditional studies of land suitability ýevaluation, the land units fit between two classes can only view one of the primary classes are ýdefined for land suitability. Therefore, the method is not able to show the continuous reality ýof land and soil spatial variability. The development of modern methods (such as fuzzy logic) ýhas solved this problem to a great extent. Therefore, the main objective of this research was to ýdetermine the optimum depth of soil for quantitative land suitability evaluation for wheat ýproduction using the fuzzy sets theory and comparison of two different fuzzification methods ýof land suitability classes in the Shahediyeh region, Yazd. ý
After crop harvesting and taking soil samples from three depths of 0 ýto 30, 30 to 60 and 60 to 100 cm in 90 observation points, and from genetic horizons of ýrepresentative pedon, which excavated in the region, the parameters needed for land suitability ýevaluation of wheat were measured. Then, land suitability classes were calculated using the ýsquare root method and were compared in three depths from 0 to 30, 0 to 60 and 0 to 100 cm. ýFuzzy calculations used for this study were conducted in two different ways. In the first ýmethod, fuzzification of land index calculated for wheat was conducted as trapezoidal fuzzy ýintervals. In the second method, firstly the variables used to calculate the land suitability ýclasses for wheat, including climatic parameters, and soil and topographic characteristics, were ýdefined as fuzzy numbers, and then the land index was calculated as a triangular fuzzy ýnumber. To obtain the numerical values of the result of applied fuzzy method (defuzzification ýprocess), the centroid method was used. Finally, to show the different land suitability classes, ýthe resulting numbers were converted to degrees of fuzzy membership. To compare the results ýof two fuzzy methods used for different depths, the similarity index that presented by Sarma, ýwas used.ý
The compatibility percentage between the results of representative pedon and ýobservation points was remarkable (more than 60 %) only for 0 to 100 cm depth. In addition, ýthe highest compatibility percentage of land suitability class was related to comparison of 0 to ýý60 and 0 to 100 cm depths in each of the two fuzzy methods. This fact shows that 0 to 60 cm ýdepth could be a relevant alternative for the optimal depth to evaluate land suitability for ýwheat in the Shahediyeh region. The results also showed that there was no difference between ýtwo fuzzy methods for all land suitability classes and at all the studied depths. ý
Overall, considering the depth of 0 to 30 and/or 0 to 60 cm in the traditional ýstudies of land suitability evaluation for wheat is not sufficient compatible with the results of ýrepresentative pedon. Therefore, if the study is not intended to offer detailed information on ýthe type of limitations for civil actions, use of the results of representative pedon to a depth of ýý100 cm based on the traditional method is sufficient and it does not need to fuzzy ýcalculations.ý