Determining root water uptake of two alpine crops in a rainfed cropland in the Qinghai Lake watershed: First assessment using stable isotopes analysis

Knowledge of crop root water uptake (RWU) is critical for understanding agricultural water management. However, the mechanisms underlying the RWU of alpine crops in rainfed cropland remain poorly understood. This study investigated seasonal variations in water uptake of oilseed rape (Brassica napus L.) and highland barley (Hordeum vulgare L.) coupled with dual stable isotope tracers at different growth stages. The method of direct inference showed that the soil depth layer from which water was predominantly taken up by roots was 0-30 cm. More specifically, oilseed rape and highland barley exhibited different RWU patterns: oilseed rape had the high flexible performance and could revert to deep soil layers (30-60 cm) as the main water source according to soil water availability due to short-term droughts at the peak growth stage. In contrast, water uptake by highland barley was primarily derived from both shallow and middle soil layers (< 30 cm) throughout all growth stages. These findings indicated that the appropriate irrigation wetting depth should be above 30 cm for the different growth stages.