284 



K. KREEB 



in very close agreement. The tendency concerning the water requirement 

 of the above mentioned crops is in hne with general observations in the 

 field. It may be of interest to note the fact that the abihty to resist drought is 

 in agreement with the salt tolerance of the plants listed in Table 3. 



The effect of salts in saline soils upon plants is mainly an osmotic one 

 (Kreeb, 1959, 1960a), therefore we have finally to discuss how the yield of 

 crops will be changed if the hydrature of the soil decreases due to salt. 

 Relatively few data are available from field experiments under natural 

 conditions. 



It is impossible to review here the comprehensive literature regarding 

 pot and solution cultures showing the effect of different salt levels on growth 

 and plant production. The following table (4) may give a general survey 

 regarding the decrease in harvested plant materials with decrease of soil 

 hydrature. The intensity of the effect differs with vegetative and reproduc- 

 tive plant parts and with different varieties of the same crop. In addition to 

 this a toxic effect, which will not be considered here, is found when different 

 kinds of salts are used in the experiments (see experiment with wheat by 

 Webster and Viswanath in Table 4). Because the plants were harvested 25 

 days after sowing, these figures may be regarded as only correct to a certain 

 extent. For practical purposes it is important to know the fmal effect on 

 harvested products. 



Some interesting results were reported in mimeographs distributed by the 

 Development Board, Baghdad (1958), showing results found by Dutch 

 scientists: It can be seen with barley (Fig. 10) that increasing conductivity 

 of solutions prepared from saturated soil (meaning decreasing hydrature) 

 causes diminution of production (grains). It appears that again the first 



600 



o 

 Saoo 



5^ 



2 



200 



O 5 10 15 20 25 



Conductivity of saturation extract in mmhos/cm 



Fig. 10. Curve of decreasing yield of barley (Murakish) with decreasing hydrature in 

 soil, expressed as conductivity of saturation extract. After Development Board Baghdad 

 1958. 



