Transpiration-use efficiency, the ratio of biomass (Y) produced per unit of water transpired (T) by a crop, depends on crop characteristics and on the environment in which crops develop. Transpiration-use efficiency has been described as Y/T = kc/Da, where kc is a crop dependent constant and Da is the daytime air vapor pressure deficit. Our objectives were to determine Y/T and kc of barley grown in Pullman, WA, and to analyze the variation in Y/T and kc of barley (Hordeum vulgare L.) and wheat (Triticum aestivum L.) reported in the literature. Transpiration and biomass accumulation of barley crops were measured in the years 2000 and 2001. The coefficient kc was estimated as the slope of the regression between cumulative values of biomass and T/D a. It ranged from 6.6 ± 0.4 to 6.9 ± 0.2 Pa. These figures are greater than 5.8 Pa obtained by applying equations developed by Tanner and Sinclair [Tanner, C.B., Sinclair, T.R., 1983. Efficient water use in crop production: research or re-search. In: Taylor, H.M., et al. (Eds.), Limitations to Efficient Water Use in Crop Production. ASA, Madison, WI, pp. 1-27]. Data on kc reported in the literature, although scarce, ranged from 3.0 to 5.9 Pa for barley, and from 2.8 to 6.7 Pa for wheat, with the lower values occurring at low Da (<1 kPa). This variability seems to associate with the response of the internal (leaf) to external (bulk air) CO2 concentration ratio (ci/ca) to changes of the leaf-to-air vapor pressure deficit (D1), suggesting that k c rather than a constant could be a function of D1. The evaluation of more field data on kc, the field validation of the response of ci/ca to D1, and testing this approach for different species and cultivars is needed to improve the understanding of the Y/T determination at the canopy level.
All Science Journal Classification (ASJC) codes
- Global and Planetary Change
- Agronomy and Crop Science
- Atmospheric Science