48 



SOIL CONDITIONS AND PLANT GROWTH 



coefficient is found to vary from year to year with the external 

 meteorological conditions, being greatest in dry years and 

 lowest in wet years ; it is also higher in wet soils than in dry 

 ones. Toulaikoff considers that it is these conditions, rather 

 than the biological character of the plant, that determines the 

 magnitude of the coefficient (284). 

 Some of his results are : — 



The year 191 1 was excessively dry, 191 3 was very rainy: 

 1 91 2 was an average year and 1914 was rather dry. 



The effect of variations in water and food supply on the 

 water requirements of plants was studied by Hellriegel, and 

 subsequently by von Seelhorst at Gottingen (256-258), who 

 has worked extensively at the various water relationships of 

 plants. His results with oats are given in Table X. 



Table X. — Effect of Varying Water Supply ^ and Food Supply on the 

 Water Requirements of Oats. Von Seelhorst (257a). 



No manure 



Complete 

 manure . 



Dry Matter Produced, 

 Grams. 



Soil 

 Moist. 



39-6 

 49'9 



Soil 

 Moister. 



86-7 



Soil 



still 



Moister. 



52-6 

 95-1 



Total Water Transpired, 

 Grams. 



Soil 

 Moist. 



10-215 

 II-170 



Soil 

 Moister. 



15-245 

 20-490 



Soil 



still 



Moister 



16-290 

 23 030 



Water Transpired per 

 Gram of Dry Matter. 



Soil 

 Moist. 



259-9 

 225-1 



Soil 

 Moister. 



312-9 

 236-8 



Soil 



still 



Moister. 



307-1 

 231-6 



^ The variations in water supply were : — 



Where 100 = saturation of the soil. 



