A Comparison of Parametric and Fuzzy Analytical Hierarchy Process (AHP) Methods to Evaluate Land Suitability for Kabkab Date Palm (Phoenix dactylifera L. cv Kabkab) Plantation in Dashtestan Area, Bushehr Province

In the assessment of land suitability, the land-production capacity is identified and the type of use is determined in proportion to that capacity. In this regard, the FAO approach has been used by many scholars in different parts of the world and Iran in land suitability assessment studies. In this approach, the most commonly used method is the parametric method. The FAO approach uses Boolean logic to assess land suitability. This logic has been criticized by a number of land evaluation researchers. Because it does not take into account the continuous nature of the soil variations along the earth's surface and the uncertainty in the measurements. To overcome these shortcomings, the fuzzy analytical hierarchy process (FAHP) was presented to determine the land suitability classes. Land suitability should be determined based on a fuzzy analytical hierarchy process, in which, unlike the FAO method, unequal importance for different land characteristics and continuity of soil variations are considered. This research was carried out with the aim of qualitative land suitability evaluation in Dashtestan area, Bushehr province for Kabkab date palm (Phoenix dactylifera L. cv Kabkab) plantation, using two methods of FAO parametric (second root formula) and fuzzy analytical hierarchy process (FAHP) and comparing these two methods. The study area is located in Dashtestan region, Bushehr province, Iran; between latitudes 29º 12΄ and 29º 31΄ N and longitudes 51º 09΄ and 51º 59΄ E. Its surface area is 23000 ha. The mean annual rainfall in the area is 250 mm and its mean annual temperature is 27 °C. The soil temperature and moisture regimes are hyperthermic and ustic, respectively. The physiographic unit which is river alluvial plain is very gently sloping. 80 % of the Kabkab date palm plantation is present in the study area. In order to achieve the objectives of this research, 50 date palm groves, each with an area of at least 0.5 ha and a palm of Kababab cultivar, aged 20 to 25 years, with the same management level and having different soil, were selected as observation points. Then a soil profile was dug randomely in each date palm grove, with dimensions of 1.5 (length), 1 (width) and 1.5 (depth) meters and described, using soil profile description guide. Soils were sampled from different horizons of the profiles and the required physical and chemical analyses were carried out on the samples, according to the standard laboratory methods. The drilling site was chosen to have a date palm tree in each of the four corners of the profile. The yield of the four trees located in four corners of each profile was measured and their average yield was considered as the final yield for the corresponding profile. Meteorological data was collected for a 10 year period from the nearest synoptic station (Borazjan station, Borazjan, Bushehr). Land indices were calculated, using soil and climatic data and parametric (second root formula) and fuzzy AHP methods. Weighted average of the climatic and the soil data was used and finally a land index was calculated for each soil profile. In the fuzzy AHP method, relative weight of each of the studied criteria was determined by analytical hierarchy analysis with establishment of pair wise matrix. Degree of membership for each soil and climatic criteria was also determined through membership functions and finally, land suitability classes were determined. At the end, accuracy of the methods was also compared. Landscape characteristics such as slope, drainage and soil depth were not considered in the land evaluation, because these characteristics did not show any limitation for the date production in the study area. The results of qualitative land suitability evaluation based on fuzzy AHP method showed that 96.6 and 3.4 percent of the studied area are classified as S2 and S3, respectively. This is in the case that based on parametric (second root formula) method, 82 and 18 percent of the studied area are marginally suitable and non-suitable, respectively. According to these results, higher land suitability classes were obtained, based on fuzzy AHP than through parametric method. Correlation between the calculated land index and the measured yield, determined for the fuzzy AHP method was higher than the one obtained for the parametric method. This proves that the fuzzy AHP is a more appropriate method for land suitability assessment for Kabkab date palm plantation in the studied area than the parametric method (second root formula). According to the results of this research, the fuzzy AHP is a more appropriate method for qualitative land suitability evaluation than the parametric method (second root formula) for Kabkab date palm plantation in the studied area in Bushehr province.