Submitted to: Agricultural and Forest Meteorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/1/2004
Publication Date: 6/1/2005
Citation: Kemanian, A.R., C.O. Stockle, D.R. Huggins. 2005. Transpiration-use efficiency of barley. Agricultural and Forest Meteorology. 130/1-2:1-11.
Interpretive Summary: Background: Modeling crop growth is a fundamental goal for predicting environmental effects on yield. An important aspect of many crop models is the calculation of transpiration'use efficiency, or the amount of crop biomass produced for a given amount of water that is used and transpired by the crop. Description: Transpiration and biomass accumulation of barley were measured in 2000 and 2001. These data show that a commonly applied constant in the calculation of transpiration-use efficiency is actually a variable with a range that is dependent on atmospheric conditions. Impact: Our results improve the understanding and calculation of transpiration-use efficiency by explaining variation in factors used to estimate this variable. The reported results and approach can be used to improve the modeling of growth and yield of barley and other cereal crops.
Technical Abstract: 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/Da. 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 (1983). 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 (Dl), suggesting that kc rather than a constant could be a function of Dl. The evaluation of more field data on kc, the field validation of the response of ci/ca to Dl, and testing this approach for different species and cultivars is needed to improve the understanding of the Y/T determination at the canopy level.