278 



K. KREEB 



first increase of the osmotic value above the optiniulm (=owest value 

 found under best water conditions and at a certain location and species) 

 lowers the production of plant material (vegetative and generative parts) 

 relatively more than at higher osmotic value levels. 



Also most of the yield data given by Bauman (i955) follow the same 

 principle after being plotted against average osmotic values (Fig. 3). They 

 are calculated as mean between numerous measurements during the 



12 





50 10 



AO 8 



30 6 



20 4 



10 2 



O O 



□ 1 Sugar bezt 

 • 2 Alfalfa 1st cut 

 3 Alfalfa 2nd cut 

 4 A Mountcalm barley 



A 



^ 4 SEagle oats 



V 7 6 Potatoes 





3 



100 500 



SO AOO 



60 300 



AO 200 



20 100 



12 



16 20 2A 28 



Average osmotic value in atm 



Fig. 3. Curves of decreasing yield with increasing average osmotic values in various 



crops. After Bauman, 195 5- 



vegetative period. The yearly curves of the osmotic values are clearly 

 related to the intensity of irrigation (Fig. 4) : i.e. the decreasing water 

 availabihty causes an increase in the osmotic value. At the termination of 

 the experiment we found the highest osmotic value (more than 25 atm) 

 at the plots (S 4) with smallest amounts of irrigation water (76-5 mm). 

 Plot S I with 'optimum hydrature conditions' (288 mm irrigation water) 

 showed contemporarily a value between 14-16 atm, and the plots S 2 

 (127-7 mm) and S 3 (84-2 mm) more than 16 atm and approximately 19 

 atm respectively at the same time. 



It was interesting to observe in this experiment that the decrease of the 

 yield at lower hydrature conditions depends on the dinoinution of the 

 number of grains more than on size of the caryopsis. The seeds ripen fully 

 even under very poor water conditions which means that the reproduction 



