Calcium nutrition and climatic conditions

The climatic conditions are one of the most striking differences between the growing conditions of field crops and those of protected crops, especially in the moderate climate zones. The increased temperature and the humidity in greenhouses are the dominating factors responsible for the differences. The radiation and the CO2 level in greenhouses are lower, when not artificially adjusted Bakker (1991). Another striking difference between the cultivation under protected conditions in comparison with cultivation in the open field is the crop production under poor light conditions in moderate climate zones. Cultivation of most crops is impossible under field conditions in these climate zones in the period from late autumn until early spring, because of too low outside temperatures. However, under protected conditions crop production occurs year round in moderate zones, which includes production under winter conditions. Heating, and possible artificial lighting contribute to successful crop productions in winter, but the growing conditions differ strongly from those during summer. The low light intensity in combination with a high humidity and relatively high temperature stimulate the vegetative development of plants, which induces negative effects on the quality of the produce. This results in winter time to crops with a lush growth and high water contents (De Koning, 1994).