Performance evaluation of microclimate inside naturally ventilated greenhouses for cultivation of flower crops

Naturally ventilated greenhouses of size 32 m length, 6 m width and 3.5 m side height and 5 m center height were designed and constructed for cultivation of rose, carnation and orchid under Bangalore condition. Side ventilation of 83% of floor area was provided with insect proof net of 40 nylon mesh. The shade net (green colour) of 25% cut off value was provided at a height of 3.5 m. The crops were provided with drip irrigation. The orchid greenhouse was provided with misters. The required relative humidity inside orchid greenhouse was maintained by operating the misters and also sprinkling water on the greenhouse sand floor. The side ventilations were covered with white colour shade net to retain the relative humidity and to provide the additional shade required for orchid crop. The temperature, relative humidity and solar radiation were recorded at 10 a.m, 1 p.m and 4 p.m inside the greenhouses and for ambient condition daily for the period of May 2003 to April 2004. The temperature in rose and carnation greenhouses was within + 2°C in comparison with the ambient temperature and relative humidity was higher upto 5% above ambient conditions. The day temperature in orchid greenhouse could be maintained between 25.2°C to 34.8°C throughout the year. The average relative humidity in orchid greenhouse at 10 a.m was 61 %, at 1 p.m 53% and at 4 p.m 49%. The percentage of solar radiations inside the greenhouses was 46% to 49% for rose crop, 43% to 44% for carnation crop and 23% to 27% for orchid crop of the ambient solar radiation. Under the above greenhouse microclimate conditions good crops could be maintained. The yield of orchids, rose and carnations was 70 flowers/m²/year, 160 flowers/ m²/year and 200 flowers/m²year respectively.