Daily CO2 changes monitored by an environment sensor unit in a greenhouse with bitter gourd

A non-aspirated air temperature and wind velocity sensor (NATVS) developed by Okushima et al. (2014) can measure wind velocity and temperature. The air temperature is calculated by measuring the temperature drop after heating a 30-μm-diameter tungsten wire for a short time. The wind velocity is calculated using the electrical resistance of this wire. Heat transfer to the air from the wire is calculated using the King equation. We extended the NATVS for use with incorporation with sensors of solar radiation, temperature, CO2 concentration, long wave radiation, and humidity (Extended NATVS). High-precision sensors of many kinds are necessary to increase the yield of horticulture products necessary to control the greenhouse environment appropriately and to analyze a greenhouse environment accurately. However, these are generally expensive. The extended NATVS is inexpensive. Using extended NATVS, a case study was conducted in a greenhouse with Bitter gourd cultivation. Generally, Bitter gourd farmers in Okinawa have continued ventilation during nighttime to control crop diseases by producing a low-humidity environment in the greenhouse. In contrast, to increase yields and to maintain disease control, it is desirable to store CO2 occurring from respiration of the crop by having no ventilation during nighttime. The amount of CO2 occurring by respiration of Bitter gourd can be stored in a greenhouse at night. Moreover, it is effective that crops be illuminated during that time so that the stored CO2 can be used for photosynthesis. We used the Extended NATVS to measure environmental factors in a greenhouse. Results show that farmers must improve the timing of film opening. Although farmers must consider the effects of solar radiation, the film probably must be opened by 10:00 a.m. One benefit of this method is that CO2 storage increases approximately 10% per day compared to opening of the side film at night.