Water-use patterns of Chinese wolfberry (Lycium barbarum L.) on the Tibetan Plateau

Chinese wolfberry (Lycium barbarum L.) can efficiently ameliorate land deterioration and increase farmers' incomes on the Tibetan Plateau. Therefore, it has been widely grown in this region in the past decades. The aims of this study were to clarify the patterns of water sources and water use efficiency under 3 management practices to determine the optimal cultivation strategies. A 2-year field experiment was undertaken in a Chinese wolfberry plantation with 3 management practices, including the conventional flat planting plus surface drip irrigation (CK), flat planting with full-film mulching plus surface drip irrigation (MF) and ridge-furrow full-film mulching plus surface drip irrigation (MR). The soil moisture in shallow (0-20 cm), middle (20-60 cm) and deep (60-100 cm) soil layers were regarded as the trees' potential water sources. The IsoSource model and two Bayesian mixing models of MixSIR and MixSIAR were employed to calculate the contribution of different water sources to xylem water. The MixSIR model exhibited relatively better performance in quantifying water source contribution for different layers compared with the IsoSource and MixSIAR models. Management practices significantly altered water use patterns of the wolfberry during the growing periods. Under CK the wolfberry preferentially extracted moisture from the middle and deep layers even during rainfall and irrigation. Under MF and MR they switched more flexibly their water source between the three layers; and they used more water from shallow and middle layers when soil moisture availability increased there, which was especially true under MR. Compared with CK, the average yield of MR and WUE were found to increase by 21.5% and 17%, respectively, over the 2years period. This indicated that film mulching and ridge-furrow altered the water use strategy of Chinese wolfberry and WUE, which can inform the designing of the best management regimes. The response to tree water use in terms of soil nutrients and subsurface irrigation should be investigated to optimize field management practices, including irrigation schedules and modes.