ISHS Acta Horticulturae 747: VIII International Symposium on Protected Cultivation in Mild Winter Climates: Advances in Soil and Soilless Cultivation under Protected Environment
WINTER TIME MICROCLIMATE IN A LARGE SCALE CANARY TYPE TOMATO GREENHOUSE IN THE SOUTH OF MOROCCO |
| Authors: | H. Majdoubi, T. Boulard, A. Hanafi, H. Fatnassi, H. Demrati, A. Bekkaoui, M. Nya, L. Bouirden |
| Keywords: | greenhouse, microclimate, insect proof nets |
| Abstract:
In this study, we presented a microclimate characterisation of a tomato greenhouse during winter time. Climate conditions were measured and analysed in a 1-ha Canary type greenhouse equipped with insect-proof nets (50 mesh) and planted with a tomato crop in the Souss Valley in south Morocco. We found a strong correlation (R2=0.90) between the difference of temperature (Tia – To) and the external global radiation (Rgo) over a period of four months (November 2004 through February 2005). It appears possible to forecast the difference of temperature between inside and outside the greenhouse based only on global external radiation. The applications of such findings are important for greenhouse farmers in managing their crop requirements. Temperatures recorded at 1 m above ground level were consistently the lowest. This is mainly due to the impact of soil temperature and cultural practices. On the other hand, temperature at 4.5 m above ground level was also lower than that recorded at 2.5 m. This is in direct relation with the roof ventilation openings. Roof ventilation opening, coupled with side ventilation opening, creates a chimney effect which eliminates hot air from the greenhouse. Relative humidity was consistently higher at 1 m above ground level than at 2.5 or 4.5 m above ground level. This is in relation with low temperatures recorded at the lower level close to the ground. This finding is very important for foliar diseases. In fact, most of the foliar diseases such as Botrytis cinerea or root diseases such as Pythium sp. are favoured by higher relative humidity. During night time, there is a non significant difference between temperatures recorded at leaf level (lower and higher), fruit level or inside the greenhouse. However, during day time, our results showed that the highest temperature is recorded inside the greenhouse, followed by fruit temperature, higher leaf then lower leaf. Our results indicate that, even though the fruit and leaf were located within the same level (lower part of the plant); the temperature of the fruit was consistently higher than that of the leaf, because the convective heat exchange of the leaf is more important than that of the fruit. Practically, our results indicate that disease forecast based on inside air temperature cannot be accurate. To make such forecasting more accurate, it is strongly advised to use the temperature prevailing at leaf level. This is even more true when we know that the biology of fungal spore or that of whitefly Nympa or Pupa for example, are more linked to the temperature of the leaf boundary layer than to the inside greenhouse air. The number of hours per day during which the soil temperature is above the minimum development level for tomato, does not exceed four and a half hour per day. Actually this period, favourable for water and nutrient solution absorption, occurs in mid day. Contrary to farmer’s practice where irrigation is practiced early morning, it is advisable to delay fertigation to early afternoon, when soil temperature around the root zone is more favourable for water and nutrient solution absorption. | |
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