عنوان مقاله [English]
Introduction: Understanding the suitability of the lands is very important in terms of the ability to cultivation a particular crop. Having information in this field helps us to act more intelligently in prioritizing land allocation for the cultivation of various crops. Also, adapting the current-grown lands under cultivation of a crop selected by the farmer to the final layer of land suitability can give us an overview of the right or wrong choice of land use. This information will help agricultural policymakers to replace crops when necessary and to replace crops that have been misallocated in disproportionately desirable lands with other crops or to improve their crop management. Therefore, this study was conducted to assess the land suitability of Golestan province agricultural lands for soybean cultivation and the degree of adaptation of current soybean-grown fields to the obtained suitability layers.
Materials and Methods: This study was carried out in the agricultural lands of Golestan province with an area of 821 thousand hectares. First, the real lands under cultivation of soybean were separated using 1674 land samples taken from different crops and object-based image analysis (OBIA) method. To separate the lands under soybean cultivation in Golestan province, sentinel 2 satellite images with a spatial accuracy of 10 meters related to planting to harvesting time in 2018 were used. Then, the layers of soil, climate, and topography characteristics were provided to investigate land suitability for soybean cultivation. Climatic components including minimum, optimum, maximum temperatures, and rainfall were estimated using long-term statistics of synoptic stations in the province (maximum available statistics). Data of soil texture, nitrogen, organic matter, phosphorus and potassium, soil pH, and salinity were also received from the provincial agricultural and natural resources research center, and from the data, the soil properties map was obtained. The digital land elevation map (DEM) of the province with a spatial resolution of 20 meters was used to extract slope, elevation, and aspect maps. The process of interpolation of climatic and soil layers was performed using ordinary kriging method. The relative importance of each factor was determined through the Analytic Hierarchy Process (AHP). This was done by designing questionnaires based on AHP paired matrices and completing it by agricultural specialists. After extracting the weights from the questionnaires and preparing the classified raster layers, these layers were imported in GIS version 10.3. Combining and overlaying the layers was done by assigning AHP weight to each layer. Finally, a land suitability map was prepared for the cultivation of the soybean in the study area which, in turn, was used to determine the adaptation of current soybean fields with determined suitability classes.
Results and Discussion: The accuracy of classification by object-oriented method using kappa coefficient and overall Accuracy coefficient (0.87 and 90%, respectively) shows the acceptable accuracy of soybean land separation in this study. In the study of land suitability for soybean cultivation, the results obtained from hierarchical analysis showed that the soil criterion had the greatest effect on the site selection of soybean cultivation with a coefficient of 0.52 with respect to both climate and topography factors. The results showed that most of the fields (about 87% of total) placed in suitable class and 13% placed in a relatively suitable class. In suitable areas for cultivation, despite having the best conditions for factors such as maximum temperature, average temperature, slope, aspect, height, soil texture, soil pH, phosphorus and soil salinity, soybean production is limited by factors such as precipitation (400 to 500 mm per year), minimum temperature (10 to 12 °C), phosphorus (8 to 10, 15 to 20 mg/kg soil). In these areas, maximum yield can be achieved by managing the mentioned factors and applying desirable agricultural management. In relatively suitable areas, limitations of nitrogen deficiency (less than 0.5 mg/kg soil), organic matter (less than 2%), salinity (above 6 dS/m), slope (more than 5%), restriction of soybean cultivation due to heavy soil texture (high percentage of soil clay), potassium (less than 100 mg/kg soil), phosphorus (more than 20 or less than 8 mg/kg soil), precipitation (less than 400 mm per year), minimum temperature (less than 10 °C), slope (more than 8%) and aspect (west and north) caused relatively high land restrictions for soybean cultivation. Compatibility analysis of the current soybean fields with the suitability maps indicated that about 99% of total cultivated lands are located in a suitable class, which demonstrates the proper selection of farm locations by the farmers.
Conclusion: By considering the position of Golestan province in the production and area under soybean cultivation in the country, if it is possible to identify suitable soybean cultivation areas according to the environmental requirements of this product and identify the limitations created by the environment, more yield per area can be achieved, which will improve the agricultural economy and the level of income of the country.