Quantifying the effects of reduced irrigation on yield and water productivity of wolfberry (Lycium barbarum L.): Insights from a three-year field study and meta-analysis

Deficit irrigation may maintain or even improve crop water productivity, but its effects on wolfberry ( Lycium barbarum L.) can vary across years and environments. We combined a three-year field experiment (2018–2020) in Delingha, Qinghai, with a meta-analysis of 104 publications to assess the effects of irrigation regimes on yield, water productivity (WP), and irrigation water productivity (IWP). The field experiment was conducted with four irrigation treatments: local conventional irrigation (CI, 300 mm, 80%CI, 240 mm, 60%CI, 180 mm, and 40%CI, 120 mm). The field experiment showed that yield response to 80%CI varied among years. Compared with CI, no significant yield difference in 2018–2019; yield was lower in 2020; WP and IWP of 80%CI increased by 8.1–9.7% and 15.5–22.3%. Across the meta-analysis, deficit irrigation reduced yield by 5.59% on average while increasing WP and IWP by 12.87% and 44.72%, respectively. Random forest model identified the deficit degree as the primary factor affecting crop productivity. A favorable yield–water productivity balance was associated with mild deficits under drip irrigation and with climates receiving 200–400 mm of annual precipitation and having a mean annual temperature ≤ 8°C, as well as with medium-textured soils with adequate nutrient availability. Overall, deficit irrigation can improve water productivity, but its benefits and yield trade-offs depend on local conditions. The finding provides valuable scientific insights for optimizing irrigation strategy for sustainable wolfberry production in Northwest China.