Yield, Quality and Water-Use Responses of Grass Pea (Lathyrus sativus L.) Cultivars to Different Irrigation Levels

This study investigated the effects of five irrigation levels (M0, M25, M50, M75 and M100) on grain yield, grain quality traits (crude protein, crude cellulose, crude ash, NDF and ADF), water use efficiency and yield–water relations of five grass pea (Lathyrus sativus L.) cultivars (GAP Mavisi, Karadağ, İptaş, Eren and Gürbüz) under the semi-arid conditions of Central Anatolia. The experiment was conducted under drip irrigation in a split-plot design with three replications, with irrigation levels assigned to main plots and cultivars to subplots. Irrigation significantly increased grain yield, which rose from 1302 kg ha⁻¹ under rainfed conditions (M0) to 2304 kg ha⁻¹ under full irrigation (M100). Crude protein, crude cellulose, crude ash, NDF and ADF increased relatively under water deficit, revealing a distinct yield–quality trade-off. The irrigation × cultivar interaction was significant for grain yield and ADF, indicating that cultivars differed in their response to water supply. Seasonal crop evapotranspiration (ET) increased from 142 mm at M0 to 393 mm at M100, whereas water use efficiency (WUE) reached its highest value under water deficit. The FAO-33 yield response factor was determined as ky=0.66 (<1), demonstrating that grass pea is relatively tolerant to water deficit. The findings indicate that moderate deficit irrigation is a suitable strategy for Central Anatolia, where water resources are limited, providing acceptable yields together with substantial water savings.