The viticultural sector is one of the most important components of Iranian agriculture, with Qazvin Province recognized as a major center for the production of high-quality table grapes and raisins. However, increasing water scarcity, climate change, and soil degradation have intensified the need for sustainable land-use planning and precise identification of areas suitable for vineyard expansion. In recent decades, vineyard development has frequently occurred without comprehensive scientific land evaluation, resulting in cultivation on marginal lands where salinity, sodicity, poor drainage, and unfavorable soil characteristics have reduced productivity and accelerated environmental degradation. Consequently, accurate assessment of land suitability has become essential for improving production efficiency while protecting natural resources. The objectives of this study were to evaluate the suitability of irrigated lands in Qazvin Province for grape cultivation, identify the principal environmental constraints limiting vineyard productivity, and determine priority areas for sustainable viticultural development. The results provide a scientific basis for optimizing land allocation, improving resource management, and supporting evidence-based agricultural planning.
The study was conducted throughout Qazvin Province, covering approximately 15,623 km². Elevation ranges from nearly 1,100 m in the central plain to more than 4,100 m in the northern Alborz Mountains, creating considerable climatic and topographic variability. The climate is predominantly arid to semi-arid, with annual precipitation varying from approximately 210 mm in the southern lowlands to more than 550 mm in mountainous regions. A comprehensive geospatial database was developed using ArcGIS 10.8 by integrating climatic, topographic, and soil information. Land suitability was evaluated according to the FAO framework for land evaluation combined with the parametric square-root method of Sys et al. (1993). This approach was selected because it effectively integrates multiple soil and climatic variables while ensuring that the most limiting factor exerts the greatest influence on the final suitability index. Unlike additive methods, the square-root model minimizes the compensation effect, thereby providing a more realistic representation of land capability under field conditions.
Meteorological records covering a 30-year period, including temperature, rainfall, and climatic indices, were integrated with detailed soil survey data. Soil profiles were evaluated for effective rooting depth, texture, gravel content, drainage, electrical conductivity of the saturation extract (ECe), sodium adsorption ratio (SAR), soil reaction (pH), calcium carbonate equivalent, gypsum content, organic carbon, and cation exchange capacity (CEC). Each characteristic was rated according to grape ecological requirements using a standardized scale ranging from 0 to 100. Individual ratings were combined through the parametric square-root equation to calculate the Land Suitability Index (LSI), and land units were subsequently classified into Highly Suitable (S1), Moderately Suitable (S2), Marginally Suitable (S3), and Not Suitable (N) categories. Suitability maps were generated to illustrate the spatial distribution of productive potential and major environmental constraints across the province.
The overall climatic suitability index of the province was 65, corresponding to the S2 class, indicating that climate is generally favorable but not optimal for grape production. A total of 254,836 ha of irrigated agricultural land were evaluated. Approximately 70.75% of the assessed area belonged to suitable classes, whereas 29.25% was classified as unsuitable. Highly suitable land (S1) occupied only 72.75 ha, representing merely 0.03% of the total evaluated area, demonstrating that naturally ideal conditions for vineyard establishment are extremely limited. Moderately suitable land (S2) covered about 140,400 ha (55.66%), while marginally suitable land (S3) occupied approximately 38,005 ha (15.07%). Unsuitable lands were divided into N1 (32,472 ha; 12.87%) and N2 (41,307 ha; 16.37%). The predominance of S2 land indicates that future vineyard development will depend primarily on effective soil and water management rather than expansion into naturally optimal environments.
concentrations of unsuitable land were identified in Buin Zahra and Abyek counties, where high soil salinity, sodicity, shallow soil depth, coarse texture, and inadequate drainage collectively restricted grapevine establishment and productivity. Climatic limitations, particularly temperature regime and growing-season length, represented the most influential constraints affecting the overall suitability index, followed by soil salinity and sodicity, physical soil properties, and drainage conditions. The dominant climatic subclass was S2c, covering nearly 98,000 ha, indicating that moderate thermal limitations affect extensive parts of the province. These findings emphasize that favorable soil properties alone cannot guarantee high productivity when climatic conditions or other limiting factors remain suboptimal. Likewise, soils with acceptable climatic conditions may still exhibit reduced suitability because of excessive salinity, poor drainage, or shallow effective rooting depth. The spatial variability observed across the province highlights the necessity of site-specific management rather than uniform agricultural practices.
The predominance of moderately suitable land demonstrates that considerable opportunities exist for improving vineyard productivity through appropriate soil and water management interventions. Areas classified as S2 possess sufficient production potential provided that their principal limitations are adequately addressed. Recommended management practices include installation of subsurface drainage systems in poorly drained areas, application of gypsum and organic amendments to reclaim sodic soils, implementation of efficient irrigation scheduling, improvement of irrigation water quality, and periodic leaching to reduce salt accumulation within the root zone. Furthermore, selection of grape cultivars and rootstocks with enhanced tolerance to salinity, drought, and thermal stress would substantially improve long-term productivity and resilience. Precision agriculture technologies, including GIS-based monitoring, variable-rate management, and periodic reassessment of soil conditions, may further increase resource-use efficiency while minimizing environmental impacts. These integrated management strategies can enhance the productive capacity of moderately suitable lands while preventing their gradual degradation into marginal or unsuitable categories.
The generated suitability maps provide valuable decision-support tools for policymakers, agricultural planners, and extension services by identifying priority areas for vineyard expansion, rehabilitation, and conservation. Rather than encouraging cultivation in environmentally fragile locations, the results indicate that sustainable development should focus on improving the productivity of existing agricultural lands through evidence-based management. This strategy not only increases agricultural efficiency but also reduces pressure on vulnerable ecosystems and conserves soil and water resources. Because climate change is expected to modify temperature patterns, evapotranspiration rates, and water availability during coming decades, periodic updating of land suitability assessments will be essential to maintain sustainable vineyard production. Integration of future climate scenarios with soil information will improve long-term planning and enable proactive adaptation strategies.
Overall, this study demonstrates that although Qazvin Province possesses substantial potential for grape production, this potential is largely conditional upon effective management of climatic and edaphic constraints. The combination of FAO land evaluation principles, the parametric square-root method, and GIS spatial analysis provided a robust framework for quantifying land suitability and identifying the principal factors limiting vineyard development. The resulting suitability maps establish a reliable scientific basis for sustainable land-use planning and investment prioritization. Adoption of the proposed management recommendations can substantially improve vineyard productivity, enhance resource-use efficiency, mitigate soil degradation, and strengthen the resilience of viticulture under changing environmental conditions. The methodological framework developed in this study is readily applicable to other arid and semi-arid regions facing similar soil and climate constraints and therefore represents a valuable tool for sustainable agricultural planning beyond Qazvin Province. By integrating spatial analysis with quantitative land evaluation, this research contributes to evidence-based decision making and supports long-term environmental sustainability while maintaining the economic viability and international competitiveness of Iranian viticulture