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 =
kDa Da-1 and; 2)
w =
kETo ET0-1 where
kDa and
kETo are crop-dependent parameters, with the underlying concept that
normalization by D
a or ET
0 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
kDa and
kETo
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,
kDa and
kETo. The results
indicated that
kDa and
kETo were more variable than expected; suggesting that calibration would be desirable. A consistent
trend of change of the parameter values as function of
Da or
ET0 was found, which can be represented by mathematical
functions, allowing transferring
w,
kDa and
kETo (maize). In contrast, the
kETo for wheat correlated weakly with
Da and
ET0,
but a low overall coefficient of variation (10%) allowed using an average value as a reasonable predictor of
w.
