Development of erosion hazard index-based land suitability criteria for sustainable agriculture in the Nilgiris hills of India

Land suitability analysis is vital for sustainable agriculture in fragile mountain ecosystems such as the Nilgiris. Earlier assessments, based on existing criteria, often rated large areas as "not suitable" and identified no "highly suitable" land for crops like potato, cauliflower, beans, wheat, and tea, despite their long history of successful cultivation in the region. This clear mismatch highlighted the need for region-specific criteria. This study refined the FAO land evaluation criteria by introducing an erosion hazard index (EHI) that jointly integrates slope gradient and active land management conditions, particularly terracing, into a single normalized parameter. To the best of the authors' knowledge, this combination has not previously been formalized for mountain agro-ecosystems of the Western Ghats. Additional adjustments to climatic and soil parameters were made to reflect the unique agro-ecological conditions of the Nilgiris. The revised assessment produced results more consistent with on-ground reality. Tea exhibited high and moderate suitability across 37.4% and 44.4% of the representative watershed (Thambatti), respectively. Potato, cole, and root vegetables were highly suitable in 6.9% and moderately suitable in 8.2% of the area, with suitability primarily limited by high erosion hazard (EHI > 0.54 for potato; EHI > 0.62 for cole and root vegetables). Field beans showed no highly suitable area but were moderately suitable in 23.4% area, constrained mainly by soil acidity, while wheat exhibited 15.1% moderately suitable area, limited by temperature, with erosion also being a significant factor for both crops. Fruit crops were moderately suitable in 12.6% and marginally suitable in 80.3% of the area, mainly constrained by low mean temperature, high soil acidity, and heavy soil texture. The refined criteria offer a more accurate and practical assessment of land suitability, addressing observed discrepancies and supporting sustainable agricultural planning in the Nilgiris.