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Estimating Reference Evapotranspiration Using Penman-Monteith (FAO-56-PM) Method from Limited Data in Fan and Pad Greenhouses

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Gaafer A. M. A., Mohammed H. I., Elfadil A. D.
World News of Natural Sciences
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2024
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vol. 53
49-59
EN
ABSTRACT Determination of reference evapotranspiration (ETo) in required for design, management and scheduling of irrigation water in fan and pad greenhouses. In actual practice estimation of (ETo) in fan and pad greenhouses is often made using the Penman-Monteith FAO-56-PM; method from external meteorological data. This requires availability of accurate meteorological input data (temperature, relative humidity, wind speed, and solar radiation). This is constrained by lack of such data which is a common problem in developing countries. In this study the proposed procedure to estimate ETo is based on using limited data of outdoor historically recorded climate elements of only temperature wind speed, and site characteristics (altitude, latitude and sun shine hours). In the proposed method radiation is to be predicted from data of air temperature difference rather than its direct measurement. This because radiation measurement using pyranometers and net radiometers is borne to errors calibration errors commonly plagued by hysteresis, and nonlinearity. The obtained results of the proposed alternative procedure were statistically validated in comparison with the standard method (FAO 56 PM) using unlimited input data measured inside the greenhouse and in reference to a directly measured ETo values by class-A-evaporation pan. The performance of the developed model was evaluated by the determination coefficient of the regression "R2 for goodness-of-fit" and by using the Root Mean Square Error (RMSE). The needed data is collected during three years in three sites in Khartoum North-Sudan El Alafoon, Halfaya, and Shambat. In each site three greenhouses were employed, and data is taken every three days for three months in each year. The obtained result reveals that the proposed limited data procedure to estimate the ETo inside greenhouses agree on statistical basis well with both pan measurement and PM estimation from measured indoor climate variables. The study reveals importance of temperature data for estimating ETo in greenhouses and calls for insuring high quality temperature data for calculating ETo in fan and pad greenhouses.
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Estimation of reference evapotranspiration inside fan and pad greenhouse from external climate data

100%
Gaafer A. M. A., Mohammed H. I., Elfadil E. A. D.
World News of Natural Sciences
|
2024
|
vol. 54
133-145
EN
With increasing cultivating areas using greenhouses, estimating reference crop evapotranspiration (ETo) inside a greenhouse has recently gained greater attention for the design of new greenhouses or for improving operation of existing ones. Currently, calculating ETo inside a greenhouse using the Penman-Monteith formula recommended by FAO is difficult because the wind speed in a greenhouse is very low or approximate zero. In addition estimating the inner greenhouse is confronted by lack of all needed climate input variables in many areas especially in developing countries. To simplify calculating the inner greenhouse ETo from the routinely and historically collected data outside the greenhouse in the study area by the Penman-Monteith formula (PM-56), a correction factor is proposed in this study. The parameters for constructing the proposed adjustment factor were taken from ETo values measured using class A evaporation pan, and from ETo determined through meteorological data. The first is used for developing and validating the proposed correction factor where data was collected during three years at three study sites (Abu Halima, Date Palm Shambat Site, and Khartoum University farm) with three greenhouses per site. In the second experiment one house is chosen in Shambat area during the third year and equipped with needed equipments. The second experiment was used for verification purposes. In all cases the fitted values by the correction factor agreed well according to statistical evaluation parameters (Chi-squire test, Mean Absolute Error (MAE), correlation coefficient (r2), the slope of the regression and the absolute deviation) with a measured value. Hence, the developed correction factor can be used as easy mean of calculating the ETo inside a greenhouse because historically available meteorological factors are needed. The estimations of the greenhouse indoor ETo PM from outdoor ETo PM could enhance climate-smart agriculture applications in semiarid environments while minimizing in-greenhouse meteorological data requirements.
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