Transpiration efficiency of rice (Oryza sativa L.)

Transpiration efficiency (TE), defined as the total dry matter produced per unit of water transpired, is an important crop characteristic, especially when water resources are becoming scarcer in many regions. But, in contrast to other major food crops, very little is known about the TE of rice (Oryza sativa L.) and its dynamics in relation to climatic conditions in typical rice environments. To close this knowledge gap, we characterized rice TE in several experiments with varying experimental and climatic conditions. All six experiments were pot studies conducted between 1994 and 2006 at the International Rice Research Institute, Los Baños, Philippines. Between experiments, arithmetic means of TE varied from 1.8 to 4.7 g dry matter per liter transpired, whereas linear regressions showed TE means between 2.2 and 4.0 g dry matter per liter transpired. Actual TE values were estimated to be about 10% higher because root biomass was not determined. The corresponding k-factor ranged from 1.4 to 5.1 Pa (arithmetic mean) and 1.3 to 5.0 Pa (linear regression slope), indicating a considerable effect of climatic conditions on CO2 and water vapor diffusion processes at the leaf surface. The analysis of different experimental treatments could not show a significant effect of drought treatments or variety on TE, but significant effects of soil type and water by nutrient interactions were observed. We concluded that the TE of rice is in the lower range of other small grain cereals, possibly comparable to oat. The results of this analysis can serve as a reference for further work on the TE of rice but they need to be verified in studies covering a wider range of climatic conditions and in field experiments.