Abstract
The objective of this study was to monitor air Vapor Pressure Deficit (VPD) in a tropical lowland shelter- house plant production. A custom-designed real-time Data Acquisition (DAQ) system with three independent microcontroller boards and sensors for monitoring aerial parameters was developed, calibrated and tested. Sample temperature and Relative Humidity (RH) data for VPD calculations were continuously collected every 60 sec, for 6 days, inside a 40 m 2 shelter-house located at the Universiti Putra Malaysia agricultural experimental field. Preliminary results showed that VPD values varied from 0.16 to 2.51 kPa, with a mean of 0.83 kPa and standard deviation (Std) of 0.6 kPa. Different regression models were used to describe the nonlinear correlation that existed between temperature and VPD data. Results showed that squared polynomial model produced the maximum coefficient of determination (R 2 ) equal to 0.976. This model was successfully used for VPD prediction based on temperature inputs. The hypotheses that collected data follow normal distribution and have different means in the 6 days of experiment were rejected at any significant level. The result of this study can be used in decision support systems' database for controlling tropical lowland plant production environments.
Highlights
Controlled Environmental Plant Production Systems (CEPPS) with fully covered transparent material are widely used in Tropical Lowland (TL) regions; the excess heat imposed by the direct solar radiation cause substantial amount of increase in the inside temperature and ambient Relative Humidity (RH)
The combined temperature and RH sensors were placed inside Okra (Abelmoschus esculentus) plants canopy (Fig. 8) that had been planted in three rows of total 15 polybags in the shelter-house
This research study provided a better understanding of TL environments by addressing relatively long-term trends in temperature, RH and Vapour Pressure Deficit (VPD)
Summary
Controlled Environmental Plant Production Systems (CEPPS) with fully covered transparent material are widely used in Tropical Lowland (TL) regions; the excess heat imposed by the direct solar radiation cause substantial amount of increase in the inside temperature and ambient Relative Humidity (RH). Ajwang and Tantau (2005) reported that under humid tropical climatic conditions, increase in temperature can rise to 38°C. Controlled Environmental Plant Production Systems (CEPPS) with fully covered transparent material are widely used in Tropical Lowland (TL) regions; the excess heat imposed by the direct solar radiation cause substantial amount of increase in the inside temperature and ambient Relative Humidity (RH). Ajwang and Tantau (2005) reported that under humid tropical climatic conditions, increase in temperature can rise to 38°C. In order to take into account both temperature and (RH) measurements, calculating the difference between the actual air moisture and its saturated point, denoted as Vapour Pressure Deficit (VPD), is of interest. Several methods for estimating vapor pressure deficits and RH have been analyzed in the study of Castellvi et al (1996)
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