Modeling Microclimate of Naturally Ventilated Greenhouse under Cropped Conditions in Soilless Media
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Date
2018
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Punjab Agricultural University, Ludhiana
Abstract
A study was undertaken to develop mathematical models for simulating microclimate of a naturally ventilated greenhouse under cropped conditions and develop the optimal operating microclimatic conditions for drip fertigated cucumber crop in soilless media. Cucumber crop was grown in coco-peat in a split plot design in three replicates during two successive growing seasons of 2016-17. The treatments included three levels of fertigation in main plots viz. F1=100.0%, F2=85.0% and F3=70.0% of complete nutrient solution under optimal microclimatic conditions. Sub-plots included cultivars viz. V1 (Kafka), V2 (Multistar) and V3 (PBRK-4). Mathematical models for standardizing the temperature of greenhouse cover, air, plant and growing media were developed, calibrated and validated in Simulink MATLAB with a mean model efficiency and coefficient of determination values of 94.7% and 0.96 respectively. Mathematical models of sensible and latent heat balance were developed to predict vertical air temperature profile and vapour pressure and solved analytically. Models for predicting saturation vapour pressure (SVP), actual vapour pressure (AVP) and vapour pressure deficit (VPD) from internal and external climates were developed and solved in Simulink MATLAB. Further, models for predicting temperature of air, leaf, plant root-zone and relative humidity were also developed from external climate. The average fruit yield was obtained in the range of 2.4-3.5 kg plant-1 and 3.3-4.4 kg plant-1 with and without fruit thinning having lowest and highest yield under treatments F3V3 and F1V2. Crop water use efficiency (CWUE) was found in the range of 60.4-86.3 kg m-3 and 84.5-108.9 kg m-3 with and without fruit thinning respectively. The average benefit cost ratio (BCR) was computed to be 1.91 and 1.54 with and without subsidy respectively without fruit thinning. However, BCR decreased by 23.7% and 23.8% with and without subsidy respectively with fruit thinning. The developed models were calibrated and validated separately for both growing seasons and a good agreement was observed between the model predictions and observed data. Thus, the developed models successfully simulated the greenhouse microclimate. Based on microclimate modeling, the desirable range of Tapc, TL, Trz, Eapc, Irad and VPD were worked out to be 22.0-27.0°C, 20.5-25.1°C, 16.9-22.9°C, 60.0-85.0%, 100.0-169 Wm-2 and 0.53-1.10 kPa respectively for optimal plant growth and development.
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