ChileanJAR

Transpiration-use efficiency (w), defined as the ratio of biomass produced per unit water transpired, has been used to evaluate crop performance under limited water supply. However, the lack of consistency of w values through different environmental conditions has not allowed, using it as a transferable parameter. Thus, simple approaches have been developed, including: 1) w = k_Da D_a^-1 and; 2) w = k_Eto ET₀^-1 where k_Da and k_ETo are crop-dependent parameters, with the underlying concept that normalization by D_a or ET₀ would accounts for the effects of climate variations on w, while these parameters would be reasonably constant across diverse environments. The objective of this study was to assess the transferability of k_Da and k_ETo for wheat (Triticum aestivum L.) and maize (Zea mays L.). The scarcity of experimental information and discrepancy of the methodology used, justified the use of a canopy transpiration and photosynthesis model which was developed, tested, and fitted with weather data from eight environmentally different locations to simulate values of w, k_Da and k_ETo. The results indicated that k_Da and k_ETo were more variable than expected; suggesting that calibration would be desirable. A consistent trend of change of the parameter values as function of D_a or ET₀ was found, which can be represented by mathematical functions, allowing transferring w, k_Da and k_ETo (maize). In contrast, the k_ETo for wheat correlated weakly with D_a and ET₀, but a low overall coefficient of variation (10%) allowed using an average value as a reasonable predictor of w.