GROWTH AND WATER USE OF VEGETABLES 

 IN A GREENHOUSE 



J.F.BlERHUIZEN 



Instituut voor Cultuurtechnick in Waterhuishouding, 

 Wageiiingen, Netherlands 



INTRODUCTION 



Inside a greenhouse, temperature is higher and radiation lower than under 

 field conditions. Radiation therefore, shifts to a stronger and temperature 

 to a less limiting value for growth. For that reason yield response will be 

 less influenced by a variation of temperature. However, since both chmatic 

 factors are intimately correlated with each other, it is difficult to distinguish 

 the effect of each of them on growth. In spruig and autumn, vegetables are 

 cultivated under more or less the same hght intensities. In the autumn with 

 a same hght intensity, however, temperature is higher than in spring, which 

 is due to the phase lag between hght and temperature. Yield of vegetables 

 in spring as well as in the autumn have been compared, giving a relation 

 between yield, heat sum and total radiation. Such a relation is vahd only 

 if soil conditions are not Hmiting growth. 



De Wit (1958) observed that in a humid chmate the ratio dry weight 

 yield/total water use, is more or less independent of soil factors, unless 

 extreme soil conditions are present. Moreover, his results obtained in 

 experiments with containers could be compared with those obtained in 

 the field. 



From radiation and temperature data then a prognosis can be made on 

 the length of a growth period necessary for a certain yield in different 

 seasons. At the same time, it will be possible to calculate total water use 

 via the relation between the latter and total yield. From these data, values 

 for water use per day can be given for vegetables grown in various seasons 

 which might be of use for irrigation purposes. An example with lettuce 

 planted at different dates will be given. 



MATERIAL AND METHODS 



The experiments were performed in a greenhouse in the period from 1954 

 to i960. The plants were cultivated in containers with a surface area of 

 0-2 m^ and a height and diameter of 70 and 50 cm respectively. Each con- 



