Estimating Tomato Transpiration Cultivated in a Sunken Solar Greenhouse with the Penman-Monteith, Shuttleworth-Wallace and Priestley-Taylor Models in the North China Plain
Round 1
Reviewer 1 Report
"Crop transpiration (Tr), which is an important part of the soil -vegetation - atmosphere continuum system[14], accounts for approximately 70 -80% of total evapotranspiration." - not clear what these percentages refer to.
" wilting point water content of 0.22 cm 3 cm - 3" - I suggest verifying the unit The roof of the greenhouse was covered with 0.1 mm -thick polyethene film - 0.1mm? " In this study, three classical methods, the Penman-Monteith model (PM 196 model), Shuttleworth - Wallace model (SW model), and Priestley - Taylor (PT 197 model)," - Authors have introduced the abbreviations several time Is there any possibility to combine different models' predictions to get more accurate data?Author Response
The replies are written in the box, and the revised article is in the attachment!
Point 1: "Crop transpiration accounts for approximately 70-80% of total evapotranspiration." - not clear what these percentages refer to.
Reply:
Thanks for this comment. Total field or crop evapotranspiration (ET) consists of soil surface evaporation (generally referring to E) and crop transpiration (generally referring to Tr). The proportion of crop Tr to total ET mainly depends on canopy coverage and soil water status. Under soil water sufficient condition, the ratio of Tr to ET firstly increases with the increasing soil surface coverage, then maintains relative constant when the soil surface is fully covered. At the late growth stage, the ratio generally decreases with crop aging. (FAO 56 paper).
We looked over literatures and concluded that, the ratio of transpiration to total evapotranspiration varies with crops, climatic condition, field management and growth stages. At seasonal base, the ration generally ranges from 65 to 90%. For example, transpiration is usually the dominant water consumer (i.e., 65–70 percent of the seasonal total ET for irrigated crops, Tr/ET reached to its maximum, near 0.9, at the middle growth stage or when LAI reached to about 3.0 for both crops (Kang et al., 2003), and at full crop cover more than 90% of ET comes from transpiration (Allen et al., 1998)
Based on the literatures, we adjusted the data range of 70-80% to 65-90%. The revised sentence can be found in lines 61-64 of page 2 as “Crop transpiration (Tr), which is an important part of the soil-vegetation-atmosphere continuum system[14], accounts for approximately 65-70% of seasonal total evapotranspiration, even up to 90% during vigorous growth periods or under full cover condition [15-17]”
Point 2: “wilting point water content of 0.22 cm3 cm-3” - I suggest verifying the unit. “The roof of the greenhouse was covered with 0.1 mm-thick polyethylene film” -0.1mm?
Reply:
Thanks for this comment. After checking, the units for wilting point soil water content is right, it is volumetric soil water content. The soil texture in the upper 40 cm soil layer is silty loam, indicating a high portion of clay and silt particles. In this case, the soil water content at the wilting point is high.
In North China Plain (NCP), the lowest air temperature in the winter season can reach to -20 ~ -30 oC. Therefore, the thickness of the polyethylene film used to cover the greenhouse top generally ranges from 0.06 to 0.12 mm. North part in NCP generally uses thicker film to keep the inside greenhouse warm. Therefore, the data of the thickness of the covered film is right.
Point 3: In this study, three classical methods, the Penman-Monteith model (PM 196 model), Shuttleworth-Wallace model (SW model), and Priestley-Taylor (PT 197 model), -Authors have introduced the abbreviations several time. Is there any possibility to combine different models' predictions to get more accurate data?
Reply:
Thank for this suggestion. Based on the results in this study, all of the three models performed well for crop transpiration estimation, with the determination coefficient of regression line between measured and predicted crop transpiration ranging from 0.84 to 0.98, and mean absolute error of varified from 0.07 to 0.28 mm/d.
Both the SW and PT models are developed based on the PM model. The input data are the same for the SW and PM models. The PT model also uses the similar climatic data when the calibrated coefficient is considered (seeing Eqns 27 and 28). Therefore, we assumed that the combination of the three models may slightly improve the accuracy of the transpiration prediction. Further, the combination of the three models will increase three-times work than using one model, which shows low efficient calculation. The main purpose of this paper is to compare the effect and accuracy of these three methods for simulating tomato transpiration in greenhouses and to give corresponding recommended methods. Fully considering the input data, calculation efficiency and research objective, the models combination for transpiration simulation is not involved in this paper. We will try to do it in future work.
Author Response File: 
Author Response.docx
Reviewer 2 Report
My comments are as below:
Is it possible to add a figure to show the greenhouse, the field and the measurements?
The authors used the methord by Thom and Oliver to parameterize the aerodynamic resistance in the PM model (Eq. 4) by considering the low wind speed, but it seems that the bias resulted by the low wind speed for the aerodynamic resistance was not considered in the SW model (Eq. 15-18). Please supply some explanation or discussion.
The wind speed is a variable in the modified PT model. Please introduce the modification (Eq. 28) in detail. Does the low wind speed affect the results? Please supple more information of the wind speed in the site.
Author Response
The replies are written in the box, and the revised article is in the attachment!
Point 1: Is it possible to add a figure to show the greenhouse, the field and the measurements?
Reply:
Thank you very much for your suggestion. Pictures, including the inside and outside views of the greenhouse, soil matric measurement using tensiometer, microclimate measurement using an auto climate station, sap flow measurement and tomatoes, have been added to the paper (page 4, line 133-138), which also were shown below:
“Due to some unforeseen circumstances, the picture cannot be uploaded to the box, please refer to page 4 in the attachment for the picture”
Figure 1. Photos of the sunken solar greenhouse. (a) Inside view with tomato growth, (b) Outside view in winter, with front plastic cover facing south and the rolled straw cushion placing on the top of the roof, (c) Soil matric measurement using dial type tensiometer, (d) A view of the meteorological station, (e) A view of one set of sap flow gauge, and (f) A view of the growing tomato.
Point 2: The authors used the method by Thom and Oliver to parameterize the aerodynamic resistance in the PM model (Eq. 4) by considering the low wind speed, but it seems that the bias resulted by the low wind speed for the aerodynamic resistance was not considered in the SW model (Eq. 15-18). Please supply some explanation or discussion.
Reply:
Thanks for this comment and suggestion. We found that though the SW model didn’t consider the effect of low wind speed in the greenhouse, it had no obvious influence on the final simulation results.
We also qualified the effect of wind speed on the estimated transpiration when the mean base values of 0.22 m/s from November 16 to 30 in 2018 season were used. When the wind speed changed from 0.06 to 0.44 m/s with the amplitude change from 25% to 200%, the variation of the simulated value changed from 6% to 23%, indicating that the simulated value of transpiration would not be greatly affected within the variation range of the actual low wind speed in the greenhouse. This discussion can be found in Lines 541-553 in Pages 18-19, which is also shown as fellow:
“The aerodynamic resistances are needed to be calculated in the PM and SW models to simulate the tomato transpiration. The PM model used the formula revised by Thom and Oliver[40], which was more suitable for the low wind speed condition in the greenhouse. In the SW model, we qualified the effect of wind speed on the estimated transpiration when the mean climatic base from November 16 to 30 in 2018 season were used, and the wind speed changed from 0.06 to 0.44 m/s with the amplitude change from 25% to 200% based on mean wind of 0.22 m s-1. Results show the variation of the simulated transpiration changed from 6% to 23%, indicating that the simulated value of transpiration would not be greatly affected within the variation range of the actual low wind speed in the greenhouse. The high R2 of 0.96 and slope of 0.93 in the regression line between estimated and measured Tr mean the SW mod-el can be used in greenhouse under low wind condition.”
Point 3: The wind speed is a variable in the modified PT model. Please introduce the modification (Eq. 28) in detail. Does the low wind speed affect the results? Please supple more information of the wind speed in the site.
Reply:
Thanks for this comment. We revised the modified PT model to clearly show the modification process. The modification process of Eq. 28 is shown in lines 332-336 of page 9, and the added content is: “Parameter calibration process was described as follows: data in the 77 days in 2018 winter season was used, and goal was the minimum MAE, the process was solve using the ’SOLVER’ function in the Excel2018, finally, the calibrat-ed coefficients a and b in the PT model were 0.71 and 13.29, respectively.”
Since the wind speed in the greenhouse was used as the input value for parameter calibration, the effect of low wind speed on simulation result had been reflected in the final value of parameters a and b. Considering the small range of the inside wind speed (0.07 ~ 0.44 m s-1), it should be noted that the calibrated coefficients of a and b were only suitable for the simulation of the daily transpiration of tomatoes planted in the winter greenhouse. For other crops in open fields, parameters a and b are needed to be re-calibrated
Wind speed information in the greenhouse has been updated to Section 4.1 (page 10, line 400-402) and is also shown below: “The wind speed in the greenhouse was from 0.07 to 0.44 m s-1, and the daily averages in the three winters from 2018 to 2020 were 0.22, 0.29 and 0.13 m s-1, respectively. ”
Author Response File: Author Response.docx
