Optimized regulated deficit irrigation of Kentucky bluegrass in Lanzhou

Kentucky bluegrass (Poa pratensis) is widely used as the turfgrass for city landscaping in the north of China, and drought is the main factor limiting the growth of turfgrass. Typically, plants exhibit a compensation or growth stimulating effect after drought and re-watering. Therefore, study on regulated deficit irrigation methods of Kentucky bluegrass in Lanzhou is very important. In this study, we conducted repetitive treatments of ‘drought-rewatering-drought-rewatering’ during the growth season of Kentucky bluegrass, which is widely planted in Lanzhou. We analysed the evapotranspiration, turf quality, physiological index, and water consumption pattern of the turfgass during different seasons to determine the optimum irrigation. The following treatments were performed:control, 70%-80% field water holding capacity (FWC); treatment Ⅰ, 65%~56% FWC; treatment Ⅱ, 55%~46% FWC; treatment Ⅲ, 45%~36% FWC; treatment Ⅳ, 35%~26% FWC; treatment Ⅴ, 25%~16% FWC. The results showed that during spring and autumn, the treatment Ⅰ had no significant effect on the analysed indexes of Kentucky bluegrass, whereas the treatments Ⅱ and Ⅲ significantly changed all indexes, and the treatments Ⅳ and Ⅴ resulted in increases of all indexes. The treatment Ⅱ had significant effects on the analysed indexes of Kentucky bluegrass during summer, but complete recovery was noted after rewatering, while in the other treatments, the indexes were more greatly altered and complete recovery was difficult even after rewatering. Therefore, the minimum irrigation limit for Kentucky bluegrass grown in Lanzhou is 40% FWC in spring and autumn and 50% FWC in summer.