1742 SOIL PHYSICS, CHEMISTRY AND MICROBIOI,OGY 



weight of 1000 seeds was also determined and their appearance was noted 

 (steeliness or starchiness) (i). 



The results of the experiments showed that the osmotic pressure of 

 the soil solution had a marked influence on plant life. This influence was 

 already appreciable when the seeds were germinating and could be follow- 

 ed throughout the development of the plant. 



As the osmotic pressure increased, germination was retarded and til- 

 lering became less vigorous while the shooting of the corn and flowering 

 were earlier, so that the whole period of vegetation was considerably cut 

 down. An osmotic pressure of 7 atmospheres obtained by the addition of 

 sodium chloride shartened the life of plants by 7 days in 1915 and by 10 

 days in 1914. The same pressure exerted by sodium sulphate only reduced 

 the period by 4 days and the effect of nitrates were still less powerful, 

 their solutions having no appreciable effect except at higher pressures 

 altogether. 



With regard to the development of the plant and the yields of straw 

 and grain, it was found that there existed a definite optimum osmotic pres- 

 sure for each of the salts tried. The x^oint varied between i and 3 atmospheres 

 according to the different salts and was marked by maximum crop ^delds 

 and by a low ratio of straw to grain. As the osmotic pressure increased 

 above this optimum point, harmful effects became evident, the develop- 

 ment of the plant was suddenly checked and low yields of grain and straw 

 were obtained. A rise in the osmotic pressure of the soil solution caused by 

 the addition of all salts except nitrates lowered the ratio of straw to grain. 



It was established in the earlier experiments that when the pressure 

 of the soil solution is between 3 and 5 atmospheres, plants are able to make 

 the available water go further than under normal conditions. This conclu- 

 sion was fully confirmed by the experiments of 1914 and 1915. In Table I 

 are given the mean coeificients of transpiration obtained with the normal 

 soil solution and with solutions whose osmotic pressures varied from i to 

 5 atmospheres. The figures show that in general transpiration decreased 

 as the osmotic pressure increased up to 5 atmospheres. Above that limit 

 a further increase in the osmotic pressure resulted in a coefficient of trans- 

 piration higher than that for the normal soil solution. Magnesium chlo^ 

 ride did not follow this rule. The fact that Bielotourka wheat uses less 

 water per unit of dry matter produced when the osmotic pressure of the 

 soil solution rises above normal, is of the greatest importance in arid regions 

 where the climatic conditions are similar to those at the Besenchouk Sta- 

 tion. 



With the soil solution at its optimum osmotic pressure the wheat not 

 only gave maximum yields, but both straw and grain contained maxinuim 

 amounts of total and protein nitrogen. In other words, the plant was making 

 the best possible use of the nutrient substances at its disposal to produce 

 the largestjamount of grain of the best quality. Table II summarises the 

 results obtained in this connection. 



(1) See [<. Sep. 1916, No. 964. (Ed. 



