GIS-Based Land Suitability Assessment for Corn and Garlic Production in the Quiaoit River Watershed, Ilocos Norte, Philippines

Abstract

This study assessed the land suitability for corn (Zea mays L.) and garlic (Allium sativum L.) production in the Quiaoit River Watershed (QRW), Ilocos Norte, Philippines, using a Geographic Information System (GIS)–based multi-criteria approach. By integrating soil properties, topography, climate, and water availability, the analysis aimed to identify areas where each crop can be sustainably grown and to highlight key environmental constraints affecting productivity. Soil parameters, including pH, organic matter, nutrient content, texture, depth, and drainage, were combined with slope, temperature, rainfall, and aquifer capacity data, following standards set by the FAO and the Bureau of Soils and Water Management. Factor weights were assigned using the Analytical Hierarchy Process (AHP) to reflect the relative importance of each criterion for corn and garlic production. The results indicate that much of the watershed is moderately to highly suitable for corn, particularly in gently sloping areas with deep clay loam soils, favorable pH, and reliable groundwater supply. In contrast, garlic suitability is generally moderate, constrained mainly by low soil organic matter and climatic conditions that can limit optimal bulb development. Spatial analysis showed that approximately 419.5 ha are highly suitable and 7,640 ha are moderately suitable for corn, while 8,420 ha are moderately suitable and 441 ha are marginally suitable for garlic. These patterns suggest that while the QRW has strong potential for corn production, garlic cultivation requires more careful management to address soil fertility and water-related limitations. The study highlights the value of GIS-based suitability mapping as a practical decision-support tool for agriculture. Targeted improvements in soil organic matter, efficient irrigation practices, and appropriate slope management can help overcome identified constraints and enhance crop productivity. The generated suitability maps provide a clear basis for crop zoning, land-use planning, and sustainable watershed management, supporting climate- resilient agricultural development in Ilocos Norte.