Using stable isotopes to quantify water uptake from different soil layers and water use efficiency of wheat under long-term tillage and straw return practices

To quantify the water absorbed by wheat in different soil layers and improve both wheat yields and water use efficiency (WUE), a 2-year conservation tillage and straw treatment experiment was implemented. This experiment involved four tillage methods, conventional tillage (C), subsoiling (S), rotary tillage (R), and no-tillage (N), and two straw treatments, straw return (W) and no straw return (0). The hydrogen, oxygen and carbon stable isotope method was used to evaluate the water source, grain yield, dry matter quantity and WUE of wheat as well as the relationships between Δ13C values of the wheat leaves, stems, ears and yield and the WUE under different tillage and straw treatment methods at the jointing and harvest stages. The results indicated that wheat water uptake occurred mainly within the 0–20 cm (86.22 %) soil layer at the jointing stage and within the 0–20 (56.36 %) and 20–40 cm (38.74 %) soil layers at the harvest stage. Compared with those in the C-0 treatment, the dry matter quantity in the S–W treatment increased by 14.86 % and 14.20 % respectively, at the jointing stage and the harvest stage; the grain yield in the S-W treatment significantly increased by 18 % at the harvest stage (P < 0.05); the WUEt and WUEi in the S-W treatment significantly increased by 46.21 % and 45.31 %, respectively, at the jointing stage (P < 0.05); and the WUEy increased by 5.69 % and 5.54 %, respectively, at the jointing stage and the harvest stage. The Δ13C vales of the wheat leaves, stems and ears were positively correlated with the yield, dry matter quantity and WUE of wheat. In conclusion, subsoiling with straw return should be adopted as a promising strategy for improving both wheat productivity and WUE and for retaining soil water availability. The Δ13C value of wheat organs can be used to indicate changes in wheat yield and WUE.