32 



SOIL CONDITIONS AND PLANT GROWTH 



TABLE IX. EFFECT OF NITROGENOUS FOOD SUPPLY ON THE GROWTH OF BARLEY 

 IN SAND CULTURES. HELLRIEGEL. 



The figures are plotted in Fig. 3. Similar results are obtained on 

 the field plots at Rothamsted (Table X.). 



4-J-tt 



O 112 224 336 



M.gms. N supplied as Co, (NO^. 



FIG. 3. Effect of Nitrogenous Food Supply on the Growth of Barley. (Hellriegel.) 



TABLE X. BROADBALK WHEATFIELD, AVERAGE YIELDS, FIFTY-SIX YEARS, 1852-1907. 



The increasing effects produced up to a certain point by successive 

 increments of nitrogen may be due to the circumstance that the ad- 

 ditional nitrate not only increases the concentration of nitrogenous 

 food in the soil, but also increases the amount of root, i.e., of absorbing 

 surface, and of leaf, i.e., assimilating surface. The process thus re- 

 sembles autocatalysis, where one of the products of the reaction acts as 

 a catalyser and hastens the reaction. The increase does not go on 

 indefinitely because some limiting factor steps in. 



The effect of nitrogen supply on the grain is very marked. In 

 Table IX. it is seen that the grain formed, when nitrogenous food is 



