## 3 Results and Discussion
### Importance of Input Variables and Processing Methods on WUE Estimates
#### 3.2.1 Importance of Water Use Variable  
Harvested techniques are similar in that they both consider above ground biomass, but the two methods differ in their approach (water input variables), where one uses precipitation (P; HWUEP) and the other ET (HWUEPT). However, P and ET do not really correlate in this region since it is a humid region with frequent rain events [75]. This is because ET is limited by both energy and water supply [76] and frequent rain events results in ET being typically limited by energy supply which is directly related to P, creating a discrepancy between these two methods. Moreover, there is no consistency in this discrepancy. Throughout the growing season, HWUEP was greater than HWUEPT, irrespective of crop, but these differences were inconsistent between sub-periods (Table 2). For example, HWUEP was highest in alfalfa during cut 2, followed by cut 1, but HWUEPT was highest during cut 4. Similarly, HWUEP was highest during growth stage 2 in maize but HWUEPT was highest in growth stage 4. Due to the lack of agreement between these methods, it is difficult to directly compare WUE estimates made by different HWUE techniques. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & & **Date** & **HWUEP 1  & **HWUEP 1  & **EWUES 1  & **Median [**EWUEg 1  & **Median [**EWUEg 1  & **Median [**EWUEg 1  \\ \hline Maize & Growth Stage 1 & 3 May–26 June & 0.42 & 0.25 & 1.26 & 2.06 & 15.97 & 21.55 \\  & Growth Stage 2 & 27 June–18 July & 5.24 & 1.73 & 3.42 & 4.01 & 12.16 & 16.05 \\  & Growth Stage 3 & 19 July–13 Aug & 4.01 & 2.24 & 3.46 & 5.18 & 17.47 & 20.39 \\  & Growth Stage 4 & 14 Aug–11 Sept & 4.76 & 3.96 & 3.21 & 5.83 & 17.17 & 22.50 \\  & Growing Season & 3 May–11 Sept & 3.01 & 1.73 & 2.58 & 4.05 & 16.18 & 20.57 \\ \hline \hline \end{tabular}  
* HWUEP = Harvested water use efficiency using precipitation for water use variable; 5 HWUEP = Leosystem water use efficiency using evapotranspiration as water use variable processed by EddyPro/Re EddyProc 1 Median EWUEP = Median half-hourly ecosystem water use efficiency using evapotranspiration as water use variable processed by Fluxpart; 6 Median EWUEP = Median half-hourly ecosystem water use efficiency using evapotranspiration as water use variable processed by Fluxpart; 7 Median EWUEP = Median half-hourly ecosystem water use efficiency using transpiration as water use variable processed by Fluxpart.  
\end{table} 
Table 2: Growing season HWUEP, HWUEPT and EWUES and median EWUES, EWUEF and EWUEC of maize and alfalfa for the 2018 growing season. Alfalfa site was divided by cut periods, while maize was divided into growth stage periods of biomass sampling points. The growth stages for maize represented early growing season (1), accelerating mid-season growth (2), pre-reproductive phase (3) and reproductive phase (4). All WUE values are presented in mg C g\({}^{-1}\) H\({}_{2}\)O. Differences between canopy scale EWUE (EWUEC) and field scale EWUE (EWUEF) occur because they use different water use variables, T and ET, respectively (Figure 2a,c). This results in inconsistencies when comparing these techniques since different crops can have different T:ET ratios throughout the growing season. For example, in this study, median half-hourly EWUEF did not vary greatly (less than 4% difference) between species, however, median EWUEC was significantly greater in alfalfa (19%). This occurs because maize contains a higher T:ET ratio over the growing season while alfalfa's is lower (Figure 2a,c). Moreover, when examined at smaller timescales, the discrepancies between T and ET methods are greater among the different alfalfa cuts than they are for different growth stages in maize (described in more detail in a following section).