Introduction
Canola (Brassica napus L.) cultivation, as a strategic oilseed crop globally and in Iran, is of increasing importance for strengthening national food security and reducing economic dependence on imported crude oil and meal. This plant, with its high oil content and desirable quality, as well as a protein-rich meal for animal feed, offers significant potential for diversifying cropping patterns and increasing farmers' income. However, the expansion of canola cultivation, especially in regions with a history of rice monoculture such as Guilan Province, faces numerous ecological challenges. These challenges include limitations arising from specific climatic conditions after rice harvesting, the physical and chemical properties of paddy soils, which are often heavy and poorly drained, and natural land topography, which can affect water management and crop growth uniformity. Under such circumstances, the precise and scientific identification of potential and suitable areas for canola cultivation as a second crop after rice, utilizing advanced spatial analysis tools like Geographic Information Systems (GIS) and the Analytic Hierarchy Process (AHP), is practical, economical, and highly important.
Materials and Methods
This research, conducted in 2024, primarily aimed at comprehensively zoning lands in Guilan Province for canola cultivation after rice harvesting. To achieve this goal, the capabilities of GIS in managing, analyzing, and visualizing spatial data, and AHP's ability to weight criteria and support multi-criteria decision-making, were employed to match the specific environmental requirements of canola with the diverse land characteristics across the province. The research process involved several key stages. First, the fundamental agro-ecological needs of canola including thermal, moisture, and light requirements, as well as soil type in terms of texture, depth, fertility (pH, organic matter, nutrients), and land slope were accurately determined and then graded for use in the model, based on credible scientific sources and field experience. Subsequently, the required digital thematic maps, including layers of key climatic elements (such as temperature, precipitation, and radiation), physical and chemical soil properties (texture, pH, phosphorus, potassium, zinc, iron, and organic matter content), and topographic features (slope and Altitude), were prepared using available data and spatial interpolation methods. After preparing the information layers, each layer was classified and ranked according to its suitability for canola growth using the Simple Limitation Method, where the unsuitability of a single factor can limit the entire area. Then, using the AHP technique and based on expert opinions and the relative importance of each factor in canola growth and yield, appropriate weights were assigned to each environmental factor layer. Finally, the weighted environmental factor layers were integrated and overlaid in the GIS software environment to produce the final land suitability map. This map zoned the province's lands into four distinct classes: highly suitable, suitable, moderately suitable, and unsuitable for second-crop canola cultivation.
Results and Discussion
The results obtained from this spatial analysis indicated that 44% and 56% of the total agricultural lands in Guilan Province are classified as suitable and moderately suitable, respectively, for post-rice canola production, with no areas identified as highly suitable or completely unsuitable. A more detailed investigation of limiting factors revealed that deficiencies in some essential nutrients for canola including iron (Fe), phosphorus (P), and zinc (Zn), as well as unsuitable soil texture (often heavy and clayey), which leads to waterlogging and oxygen deficiency in the roots, act as major limiting factors for canola cultivation in significant portions of the study area. From a climatic perspective, the average temperature during the growing season and the occurrence of maximum temperatures during sensitive growth stages were identified as the most critical limiting parameters for canola cultivation in the province.
Conclusion
Considering the strategic importance of second cropping in Guilan Province which can significantly contribute to increasing the land-use efficiency of paddy fields, improving farmers' income, and enhancing the sustainability of the region's agricultural systems, the findings of this research have important practical applications. The precise identification of canola's environmental requirements and the location of suitable cultivation areas can play an effective role in agricultural development planning, providing sound management recommendations such as soil amelioration, nutrient management tailored to deficiencies, and the selection of resistant or tolerant varieties for areas with limitations.