Development and application of a relative soil water content – transpiration efficiency curve for screening high water use efficiency wheat cultivars

Improving water use efficiency (WUE) has been proven to be a prosperous way to produce more grain in drought-prone areas. Transpiration efficiency (TE) has been proposed as a criterion for screening cultivars with high WUE. This study quantifies the relations of TE to relative soil water content (RSWC) gradients using pot experiments and evaluates the capability of the relations of TE-RSWC on assessing the cultivar performance in field yield and WUE. Twelve winter wheat cultivars were grown at 6 RSWC, 12.1, 24.2, 36.3, 48.4, 60.5, and 72.6% of field capacity (FC = 24.8 g/g) for 33 days in tightly sealed pots preventing soil evaporation. The results showed that TE decreased power functionally following the increase in RSWC for all cultivars. The relationship could be described as TE = TE (FC) × (RSWC) (b), named TE–RSWC curve. This curve could be divided into an orderly area where the rank of cultivars was stable when RSWC ≤ 12.1% or RSWC ≥ 72.6% and a disorderly area where the rank was unstable when 12.1% < RSWC < 72.6%. To assess the consistency of pot TE to field yield and WUE, the same 12 varieties were grown under rainfed and two irrigations (75 mm at the jointing and flowering stages, respectively). TE (FC) was found to be positively related to field yield and WUE independent of irrigation. TE measured near the wilting point was negatively related to field yield and WUE. These results indicated that TE (FC) could be used as a surrogate for screening high-yield and high-WUE cultivars. The consistency and inconsistency can be attributed to the orderly area and disorderly area of the TE–RSWC curves.