Revising and Optimizing Iso-Yield Curves for the Diverse Agro-Climatic Zones of Sri Lanka

Abstract

The most recent nationwide Iso-Yield curves, which illustrate regional variations in crop productivity, were last updated in Sri Lanka in 1978. This lengthy gap in data is significant, especially given the considerable changes in climate, hydrology, and agricultural practices that have taken place over the past four decades. This study aims to update Sri Lanka's yield maps for its two primary monsoon-driven cultivation seasons: Maha (Northeast Monsoon) and Yala (Southwest Monsoon). To achieve this, an integrated approach is employed, combining river gauge data, records of reservoir operational inflows and outflows, and observed agricultural production statistics. Historical and contemporary hydrological datasets from key river basins were compiled and analyzed to estimate irrigation water availability patterns across districts. These hydrological indicators were statistically correlated with crop yield performance data derived from national agricultural statistics, facilitating the spatial interpolation of updated yield distributions. Advanced geospatial analysis techniques and GIS-based modeling were employed to delineate field zones characterized by homogeneous yield potential, resulting in the generation of updated Iso-Yield curves for both monsoon seasons. The findings indicate significant spatial shifts in high- and lowyield zones compared to the 1978 maps, reflecting the combined effects of climate variability, alterations in reservoir operations, and evolving irrigation practices. The updated Iso-Yield curves provide a more accurate representation of Sri Lanka's current agricultural productivity landscape, aiding in precise zoning for optimized agronomic decisions, targeted irrigation scheduling, and region-specific crop planning. This study offers a valuable decision-support tool for policymakers, irrigation managers, and farmers, while establishing a methodological framework for future yield mapping endeavors in monsoon-dependent agricultural systems.