## 4 Conclusions  
ETo was estimated using FAO-56, LSTM, and bidirectional LSTM at four sites of Prince Edward Island namely Saint Peters, Harrington, Summerside, and North Cape for the study period 2011-2017. Performance of the LSTMs was evaluated using the meteorological data that were split into two sets, namely training set (2011-2015) and testing set (2016-2017). Based on subset regression analysis using nine different climatic variables, the maximum air temperature and relative humidity were selected as inputs for recurrent neural networks. By using tuned hyperparameters, the LSTM and bidirectional LSTM were able to estimate ETo with considerable accuracies determined with ETo calculated using the method of FAO-56. There were no major differences in the accuracy of LSTM and bidirectional LSTM. However, for the Harrington site, bidirectional LSTM performed better in comparison with LSTM for the testing set (2016-2017). The advanced architecture of bidirectional LSTM might be helpful in attaining the higher accuracies in comparison with LSTM. Furthermore, the dataset of Harrington sites showed slightly higher standard deviation in comparison with other sites selected for this study. The results suggested that the bidirectional LSTM can achieve higher accuracy with scatter data in  
Figure 7: From bottom to top, comparison of rainfall (shown as water bubbles area chart separated from ETo-bidirectional LSTM by broken blue lines), ETo-bidirectional LSTM (shown as red vapors separated from ETo-LSTM by solid red line), ETo-LSTM (shown as solid black line), and ETo-FAO-56 (shown as broken black line) for (**a**) year 2016 and (**b**) year 2017. The curve for ETo-BLSTM is hidden under the curve of ETo-LSTM because of negligible difference between the estimates of the two models. This is why ETo-BLSTM has been drawn as an area chart of red vapors above rainfall chart and ETo-LSTM is drawn as a line chart.  
comparison with LSTM. Another objective of this study was to quantify the difference ETo and rainfall. The analysis showed that in months of June, July, and August, the ETo surpassed rainfall emphasizing the need for viable options such as supplemental irrigation to replenish the crop water requirements in drier months for agriculture sustainability of potato production in Prince Edward Island.  
Conceptualization, H.A., A.A.F., and F.A.; methodology, H.A. and F.A.; software, H.A. and F.A.; validation, A.A.F.; formal analysis, A.A.F., B.A., and T.E.; investigation, H.A. and F.A.; resources, A.A.F.; data curation, H.A., B.A., and T.E; writing--original draft preparation, H.A. and A.A.F.; writing--review and editing; B.A., and T.E.; supervision, A.A.F.; project administration, A.A.F. and F.A.; funding acquisition, A.A.F. All authors have read and agreed to the published version of the manuscript.  
This research was supported by the Natural Science and Engineering Research Council of Canada, the Prince Edward Island Potato Board, the Canadian Horticultural Council, Potato Board New Brunswick, the New Brunswick Department of Agriculture, Aquaculture and Fisheries (CAP program), and Agriculture and Agri-Food Canada.  
The authors thank and the Precision Agriculture Team at the University of Prince Edward Island for their cooperation and assistance during the experiment.  
The authors declare no conflict of interest.