256 J. F. BIERHUIZEN 



is far more important for growth in greenhouses than temperature. There 

 is a Hnear relation between total water use [x) and dry weight yield (y) of 

 the form y = mx, the constant m being dependent upon the depth of the 

 water table. Using radiation and temperature data, a prediction of a certain 

 yield or length of growth period can be made. It is possible, using total 

 radiation and heat sum, to compare yield in various greenhouses in order 

 to study the effect of glass-cover, soil type and other factors on growth. 

 The above mentioned results were obtained under optimal soil moisture 

 conditions. At present a study is in progress on the relation between yield 

 and water use, total radiation and heat sum, under various sub-optimal 

 soil moisture conditions. 



REFERENCES 



BiERHUiZEN, J.F. (i960) De relatie tussen teniperatuur en licht en de opbrengst van 



verschillende tuinbouwgewassen in kassen. (The relation between temperature, 



light and yield of various vegetables in a greenhouse. Dutch with an English 



summary.) Med. Dir. Tuinhouw, 23 (12), 822-831 

 BiERHUiZEN, J.F. & Vos, N.M. DE (1958) The effect of soil moisture on the growth 



and yield of vegetable crops. Report Conference on Suppl. Irrigation, Commission 



VI, Int. Soc. Soil Sci., Copenhagen, 83-92. Techn. Bull. Il, 1959. Inst, for Land and 



Water Management Research, Wageningen. 

 Bloemen, G.W. (i960) Het onderzoek naar de waterbalans van landbouwgronden 



(Investigations on the water balance of agricultural soils, Dutch.) Med. Cultuur- 



tcchn. Vereniging, 4 (i), 3-25. 

 BoHNiG, R.H. & Burnside, C.A. (1956) The effect of light intensity on apparent 



photosynthesis in leaves of sun- and shade-plants. Am. J. Bot. 43, 557-56i. 

 DE Vries, p. a. (1955) Solar radiation at Wageningen. Med. Landbouwhogeschool, 



Wageningen, 55 (6), 227-304. 

 DE Wit, C.T. (1958) Transpiration and crop yields. I'ersl. Landbonwk. Ondcrz. 64 (6), 



1-88. Med. 59, Instituut voor Biologisch en Scheikundig Onderzoek van 



Landbouwgewassen. 

 Gaastra, p. (1959) Photosynthesis of crop plants as influenced by light, carbon dioxide, 



temperature and stomatal diffusion resistance. Med. Landbouwhogeschool, Wage- 

 ningen, 59 {13), 1-68. 

 Makkink, G.F. (1957) Ekzameno de la formulo de Penman. Neth. J. Agr. Sci. 5, 



290-305. 

 RijTEMA, P.E. (1958) Calculation methods of potential evaporation. Report Conference 



on Suppl. Irrigation, Commission VI, Int. Soc. Soil Sci., Copenhagen, 15-24. Techn. 



Bull. 7, 1959. Inst, for Land and Water Management Research, Wageningen. 

 VisSER, W.C. (1959) Crop growth and availabiUty of moisture. Techn. Bull. 6. Inst. 



for Land and Water Management Research, Wageningen. 

 Wassink, E.C. (1948) De lichtfaktor in de fotosynthese en zijn rclatic tot andere 



miheufaktoren. (The factor hght in photosynthesis and its relation to other 



growth factors, in Dutch.) Med. Dir. Tuinbomi', II, 503-514. 



