Abstract
Irrigation of protected crops requires sound knowledge of evapotranspiration. Previous studies have established that the eddy-covariance (EC) technique is suitable for whole canopy evapotranspiration measurements in large agricultural screenhouses. Nevertheless, the eddy-covariance technique remains difficult to apply in the farm due to costs, operational complexity, and postprocessing of data, thereby inviting alternative techniques to be developed. The subject of this paper is the evaluation of a turbulent transport technique, the flux variance (FV), whose instrumentation needs and operational demands are not as elaborate as the EC, to estimate evapotranspiration within large agricultural structures. Measurements were carried out in three types of agricultural structures: (i) a banana plantation in a light-shading (8%) screenhouse (S1), (ii) a pepper crop in an insect-proof (50-mesh) screenhouse (S2), and (iii) a tomato crop in a naturally ventilated greenhouse with a plastic roof and 50-mesh screened sidewalls (S3). Quality control analysis of the EC data showed that turbulence development and flow stationarity conditions in the three structures were suitable for flux measurements. However, within the insect-proof screenhouse (below the screen) and the plastic-covered greenhouse, R2 of the energy balance closure was poor; hence, the alternative simple method could not be used. Results showed that the FV technique was suitable for reliable estimates of ET in shading and insect-proof screenhouses with R2 of the regressions between FV latent heat flux and latent heat flux deduced from energy balance closure of 0.99 and 0.92 during validation for S1 and S2, respectively.
Highlights
In recent years, the area of vegetables and orchards grown in protected cultivation systems is constantly increasing. ese include, among other structures, naturally ventilated greenhouses [1], insect-proof screenhouses [2], and shading screenhouses [3]. ese structures are naturally ventilated and have significant interaction with the external environment. e advantages and limitations of such protected cultivation systems are well documented in the literature [4, 5].Protected crops are exposed to microclimatic conditions that are significantly different from those in the open field
E most common method for direct measurements of evapotranspiration and other scalar fluxes is the eddy covariance [14]. e method was originally developed and International Journal of Agronomy mostly used for flux measurements over open surfaces like forests, natural, or agricultural fields and open water bodies
A eld experiment was carried out in 3 di erent naturally ventilated agricultural structures, two screenhouses, and a greenhouse to study the suitability of a simple turbulent transport technique, namely, the ux variance, in estimating sensible and latent heat uxes. e major conclusions of this study are as follows: (i) Quality control analysis of the EC
Summary
The area of vegetables and orchards grown in protected cultivation systems is constantly increasing. ese include, among other structures, naturally ventilated greenhouses [1], insect-proof screenhouses [2], and shading screenhouses [3]. ese structures are naturally ventilated and have significant interaction with the external environment. e advantages and limitations of such protected cultivation systems are well documented in the literature [4, 5].Protected crops are exposed to microclimatic conditions that are significantly different from those in the open field. Ese structures are naturally ventilated and have significant interaction with the external environment. Is modification may affect the evapotranspiration; that is, the water vapor flux from the canopy to the atmosphere, which, in turn, will affect the irrigation demands. E possibility of water saving through reduced transpiration and irrigation demands initiated a number of research studies focused on evapotranspiration measurements and estimates, mainly in screenhouses [3, 9,10,11,12,13]. E method was originally developed and International Journal of Agronomy mostly used for flux measurements over open surfaces like forests, natural, or agricultural fields and open water bodies. Due to its high capabilities in reliable measurements of whole canopy evapotranspiration, in recent years, its performance was examined in protected environments like screenhouses One effect of covering the crops is in modifying the exchange of energy, mass, and momentum between the plants and their environment. is modification may affect the evapotranspiration; that is, the water vapor flux from the canopy to the atmosphere, which, in turn, will affect the irrigation demands. e possibility of water saving through reduced transpiration and irrigation demands initiated a number of research studies focused on evapotranspiration measurements and estimates, mainly in screenhouses [3, 9,10,11,12,13].
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