Effects of Deficit Mulched Drip Irrigation on Water Productivity of Pepper in a Cold and Arid Environment

To assess the impact of water deficit (WD) under film-mulched drip irrigation on pepper yield and water use efficiency (WUE), a field experiment was conducted with three levels of WD: mild (65%-75% field capacity, FC), moderate (55%-65% FC), and severe (45%-55% FC). WD treatments were applied during the seedling, flowering and fruiting, full fruiting, and late fruiting stages, with full irrigation (75%-85% FC) throughout the growing season serving as the control (CK). Results showed that WD during the flowering and fruiting stages significantly reduced pepper yield by 11.68%-25.56%, fruit number per plant by 18.18%-45.45%, and single fruit weight by 17.33%-19.94% compared to CK. However, moderate WD at the seedling stage and mild or moderate WD at the later fruiting stage significantly improved WUE by 6.25%-11.61% without significantly reducing fruit yield or harvest index relative to CK. The Jensen-based crop water production function revealed that the flowering and fruiting stages, with a water sensitivity index of 0.517, are critical for pepper's water needs, emphasizing the importance of adequate irrigation during this period for higher yields. Thus, water-saving and efficient pepper production can be achieved through deficit irrigation with under-membrane drip irrigation.