Evaluation and modelling of greenhouse cucumber-crop transpiration under high and low radiation conditions |
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Affiliation: | 1. College of Horticulture, Northwest A&F University, Yangling, Shaanxi 712100, China;2. Key Laboratory of Protected Horticultural Engineering in Northwest, Ministry of Agriculture/Shaanxi Province Facility Agriculture Engineering Center, Yangling 712100, China;3. Key Laboratory for Agricultural Soil and Water Engineering in Arid Area of Ministry of Education, Northwest A&F University, Yangling 712100, China;4. College of Horticulture and Landscape Architecture, Heilongjiang Bayi Agricultural University, Daqing City 163000, China |
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Abstract: | The main objective of this study was to analyse the transpiration time course of soilless culture cucumber plants (Cucumis sativus L.) during two cycles, at low (up to 9 MJ m−2 d−1) and high (up to 20 MJ m−2 d−1) radiation levels, and their relationship with greenhouse climate parameters (incident radiation and vapour pressure deficit, VPD) and canopy development. The coefficients of the simplified Penman–Monteith formula were calibrated in order to calculate the transpiration rate of the crop, to help improve irrigation management in substrate cultivation. The transpiration rate per ground surface area was measured by weighing plants with an electronic balance.At high radiation levels, the diurnal canopy transpiration rate was four times higher than at low radiation levels and the night transpiration rate reached values between 120 and 200 g m−2 d−1 in both cases. The leaf transpiration rate decreased during crop ontogeny and was higher in the afternoon than in the morning for the same value of radiation, whereas a linear relationship with the VPD was found even for values greater than 3 kPa. The results showed that the fitted simplified Penman–Monteith formula accounted for more than 90% of the measured hourly canopy transpiration rate, signifying that this formula could be used to predict water requirements of crops under Mediterranean conditions and improve irrigation control in a substrate culture. However, the model coefficients will have to be adjusted for specific climate and crop conditions. |
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