Effects of a near infrared-reflecting greenhouse roof cover on the microclimate and production of tomato in the tropics

The effects of a shading paint containing NIR-reflecting pigments applied to the roof of an experimental greenhouse on greenhouse microclimate, plant response of a tomato crop and fruit yield and quality were studied under the tropical climate conditions of Central Thailand. One experiment was carried out in the rainy (2006) season and in the dry (2005/2006) season.The maximal reduction of the air temperatures inside the greenhouse with the NIR reflecting roof paint was observed during the dry season. At this time the temperature in this house was 2.8 °C lower than in the control greenhouse without shading paint. On average the temperature reduction was 2 °C in the dry and 0.6 °C in the rainy season. The magnitude of the temperature reduction was influenced by the time of application in relation to stage of plant growth. Cumulative water consumption between the 4th and 17th week after transplanting was reduced by 8.8 % and 6.2 % during the dry and rainyseason, respectively. However, this did not significantly influence overall water use efficiency. Reduction in the transmission of the photosynthetic active radiation did not significantly influence yield. Shading had only negligibly small influence on plant height, number of trusses, leaf area index and dry matter partitioning