GROWTH AND WATER USE OF VEGETABLES 255 



Table i 



Growth and Water use of Lettuce to a head-weight of 150 gm in different 



seasons 



Although for practical irrigation purposes other water losses than those 

 calculated in Table i, column 5, may be of greater importance, the calcula- 

 tions made in Table i make it possible to give some indications of the 

 irrigation frequency to be used for a particular crop in different seasons. 

 Assuming a root depth of 50 cm and an available quantity of water between 

 field capacity (pF 2-0) and wilting point (pF 4-2) of 12% by volume, the 

 total amount of available water is 5 x 12 = 60 mm. If one fourth or 15 mm 

 can be used without decreasing fresh weight and quality of vegetables, the 

 irrigation frequency in different months can be given, using values of pan 

 or water use per day (columns 6 and 5 respectively). 



SUMMARY AND CONCLUSIONS 



Some relations between yield, water use, temperature and radiation in a 

 greenhouse were given and discussed in this paper. It appears that radiation 



