1. Introduction: Understanding climate and soil variables will be an important step in proper agricultural planning and utilization of resources, especially in the irrigated lands of the country, which are facing the problem of water shortage today. Tomato, with the scientific name of Solanum lycopersicum, is one of the important vegetables of the Solanaceae family, which is widely and often cultivated as an annual plant and is one of the most important agricultural products in the country. Considering the sensitivity of tomatoes to temperature, basic research on this topic is crucial to reduce investment risk and water waste as a valuable resource by identifying unsuitable climate conditions for growing this product. In this regard, land suitability assessment studies provide very useful information for decision-makers. Kermanshah province is one of the prominent provinces in the field of agriculture and is the main producer of many important and strategic products. To properly use resources and increase production, and considering the review of sources that shows no study has been done to investigate the effect of temperature and soil on tomatoes which are cultivated in the irrigated lands of Kermanshah province, this study investigated the effect of temperature and soil on the performance of this product in each of the temperature classes including these lands to determine the degree of compliance of the temperature conditions of each class with the temperature requirements of this product.
2. Materials and Methods: By overlapping the shapefiles of the temperature classes and irrigated lands of Kermanshah province, the temperature classes were determined within the irrigated lands of the province. Subsequently, a synoptic station was selected in each temperature class, and for each synoptic station, climatic data were collected for a thirty-year statistical period (1991-2021). To evaluate the climate and soil for tomato suitability according to the FAO method, the tables of climatic and soil and landscape requirements of tomato developed by the experts of the Soil and Water Research Institute were used. The investigated climatic parameters included the mean temperature of the growing cycle, the mean temperature during the yield formation period, and the difference between night and day temperatures during the flowering stage. The phenological periods for each of the studied temperature classes were completed using expert knowledge and farmers’ experience in this province. Based on the phenological periods of each region and the temperature requirements table, a degree between 0 and 100 was assigned to each of the parameters. Then, the lowest grade obtained was considered equivalent to the climate index (CI), and the final climate grade (CR) was determined. The investigated soil and landscape parameters include slope, flooding, drainage, depth, soil texture and structure, coarse fragment, CaCO3, gypsum, apparent CEC, base saturation, the sum of basic cations, soil acidity, organic carbon, EC, and ESP. Soil indices (SI) were calculated using the parametric-square root method, and based on these indices, the suitability classes were determined.
3. Results and Discussion: The irrigated lands of the province fall into three classes out of the five classes of the temperature map. These classes are in order of area: cold class with a temperature between 10 and 15 ◦C, temperate class with a temperature between 15 and 18.5 ◦C, and hot class with a temperature between 18.5 and 22 ◦C. Based on the results, in the cold temperature class, the mean temperature during the flowering stage is the most limiting factor for tomato cultivation, and in the hot and temperate temperature classes, the mean temperature during the yield formation period poses the greatest constraint for the cultivation of this product. The degrees of climatic suitability calculated for cold, temperate, and hot classes were about 84, 82, and 61, respectively. Therefore, it can be concluded that the temperature potential of Kermanshah province for irrigated tomato cultivation is different in the three studied strata, and the eastern regions of the province are the most suitable areas for cultivating the crop. Hence, it is suggested that before investing in the cultivation of this product, the effect of climate on production should be considered, so that, having a perspective of the result of cultivation, appropriate policies can be adopted to prevent wrong investments and the best product can be selected for sustainable production. The most important limiting factors for the growth and production of this product in the three studied temperature classes were soil acidity, slope, drainage, and soil physical properties (texture and structure of soil and gravel). Soil acidity was the most important limiting factor in the two temperate and hot temperature classes. In the cold temperature class, slope and acidity were the two most important factors in reducing tomato production. The total percentage of the area of very suitable and relatively suitable classes in cold, moderate, and hot temperature classes is about 33, 60, and 54%, respectively. Among the cities, Kangavar, Ravansar, and Sarpol-e Zahab have the largest relative area of suitable soils (with high and medium suitability) in the cold, temperate, and hot temperature classes, respectively. Kermanshah also has lands with suitable soil in two cold and moderate temperature classes.
4. Conclusion: In Kermanshah province, in the cold, moderate, and hot temperature classes, the temperature factor will be 26%, 28, and 39% effective in reducing the yield compared to the potential conditions and moving from the east to the west of the province, the ability of the regions to cultivate irrigated tomatoes decreases, and the western regions of the province have a relatively high-temperature constraint during the yield formation period. The results of the soil suitability study showed that soil acidity and slope were the most important factors in reducing the yield of this crop in all three temperature classes. According to the results of temperature and soil suitability, it can be said that the moderate temperature class has relatively more suitable temperature and soil conditions for tomato cultivation.