Lycium barbarum root water uptake characteristics in the Qaidam Basin irrigation

Lycium barbarum (Chinese wolfberry) helps ecosystems by providing storm protection and sand immobilization, and it is also a cash crop for Qaidam Basin farmers. L. barbarum is a common crop in arid regions, such as the Qaidam Basin, China, but drought and water scarcity have constrained industry development. Identifying crop water-use strategies is important for designing efficient irrigation systems. Seasonal L. barbarum water-use was investigated in 2018 in the Qaidam Basin Huaiten Tula Irrigation Area. Natural oxygen stable isotope tracers were used to measure the oxygen stable isotope composition (δ¹⁸O) of water in the xylem and soil of L. barbarum orchards with three field management practices (conventional flat planting, CK; flat-planting full-film mulching, MF; and ridge-furrow full-film mulching, MR). The soil water contribution to root water uptake was analyzed using the MixSIAR Bayesian mixing practices. The soil water and soil water δ¹⁸O profile distribution showed that all soil layers (shallow: 0-20 cm; middle: 20-60 cm; and deep: 60-100 cm) were potential water sources for L. barbarum. During the sprouting period (starting May 25, 2018), CK and MF plants used primarily shallow soil water, accounting for 45.9% and 37.7% of the total water use, respectively, due to the larger amounts of shallow-layer soil water. MR plants used the same amount of water from each layer. During the blossom and fruiting period (starting July 9, 2018), the soil water content increased in all soil layers. Compared with that in CK plants, the shallow-layer soil water use increased by 13.5% in MF plants and decreased by 11.1% in MR plants. During the fruit ripening period (starting July 30, 2018), water consumption increased. Compared with that in CK plants, shallow-layer soil water use increased in MF (by 11.7%) and MR (by 24.0%) plants. During the defoliation period (starting September 22, 2018), the water content in the shallow-layer soil was lower than that in the other soil layers, and all of the treatment groups used primarily deep-layer soil water. These results showed that shallow-layer soil contributions were positively correlated with water content, indicating that L. barbarum is sensitive to changes in the shallow-layer soil water. There were significant differences in the root water uptake among the three field management practices. Mulching and ridge-furrow treatments increased the soil water content and, compared with that in CK plants, the MF and MR treatments increased the shallow-layer soil water use. The soil water content was higher and the water source was more flexible during the growth period with the MR treatment than with the CK and MF treatments. These results suggest that MR is a better field water management practice for promoting the sustainable and healthy development of L. barbarum orchards.