Trade-Off Between Yield and Water-Use Efficiency in <i>Piper nigrum</i>

Water-use efficiency (WUE) plays a crucial role in sustainable crop production, particularly in water-limited environments where maximizing natural resource use is essential. This study evaluated the physiological and agronomic performance of two <i>Piper nigrum</i> cultivars, Clonada and Uthirankotta, grown under different soil water potential conditions. The trial was conducted in a 1930 m² field using a randomized block design and drip irrigation system, calibrated to 3.55 L h⁻¹ with a uniformity of 97%. Soil water availability was managed based on daily tensiometer readings at 20 and 30 cm depths, triggering irrigation at defined tensions (10–55 kPa). Clonada exhibited higher net CO₂ assimilation rates (<i>A</i>) and stomatal conductance (<i>g</i>_s), but these responses did not lead to higher yields. In contrast, Uthirankotta consistently maintained superior water-use efficiency and yield across all soil moisture conditions by favoring water conservation and targeted biomass allocation over maximized gas exchange. Both cultivars performed optimally at a soil water potential range of 25–35 kPa, with declines in yield and gas exchange parameters at higher tensions (45–55 kPa). Under such conditions, Uthirankotta was 51.3% more water-use efficient and 40.8% more productive than Clonada. Based on this, a Principal Component Analysis (PCA) further demonstrated distinct physiological profiles, underscoring trade-offs between yield and water-use strategies. These results highlight the significance of cultivar selection for optimizing WUE and provide valuable insights into irrigation management and breeding programs aimed at boosting black pepper performance under water-limited conditions.