ABSORPTION OF MINERAL ELEMENTS BY PLANTS 275 



growth of the vegetative organs and a general increase of the 

 plant mass, led to an increase in the absorption of mineral sub- 

 stances from the soil. 



This close connection between the accumulation of organic 

 and mineral substances explains why in arid conditions black 

 soils do not react to the application of fertihzers, while the same 

 soils and under the same climatic conditions, but with the 

 application of irrigation or in pot cultures, show a clear depend- 

 ence of the magnitude of the yield on the amount of fertilizers 

 appUed. With a deficiency of water supply, the yield on cher- 

 nozem soils depends upon the amount of available water, since 

 the amount of mineral and nitrogen substances present in 

 chernozem soils is more than sufficient to produce the maximum 

 jdeld possible with the limited water supply. But as soon as 

 the water supply is increased, as for instance by irrigation or the 

 regulation of watering in pot cultures, growth is accelerated, 

 the reserves of nutrient elements in the soil are no longer suffi- 

 cient, and as a consequence the plants are affected by the applica- 

 tion of fertilizers. 



Since the mineral elements represent chiefly regulators of the 

 vital processes, they are of great importance to the plant whose 

 growth is dependent upon the supply of these elements. In its 

 first stages of development, the plant utilizes chiefly the reserves 

 of mineral salts stored in the seeds. During this period of its 

 fife, the growth of the plant is relatively slow, and therefore its 

 requirements are not so great; but they increase rapidly up to 

 the time of the most vigorous growth, which coincides with the 

 period of blooming and the setting of fruit. The time of accumu- 

 lation of the chief mineral elements, at least of potassium and 

 phosphoric acid, corresponds in general to the time of accumu- 

 lation of organic substance. The cessation of increase of organic 

 substance during the ripening of the seed is accompanied as has 

 already been noted by a backward flow of a part of the mineral 

 elements from the plant into the soil. 



The usual methods of application of fertilizers by plowing them 

 into the soil before the sowing of seed does not fulfill the require- 

 ments of the plant. By this practice, the plant obtains the 

 maximum quantity of fertilizer elements in the first stages of its 

 development when it least requires them ; while at the time when 

 its requirements for nutrients increase, the amount of nutrients 



