Hoagland — 174 — Plant Nutrition 



mes, and no doubt the correlating action of hormone 

 substances. 



To determine by empirical means under a given 

 climatic and soil condition, for a particular crop, at 

 a particular stage of growth, that the growth of the 

 plant, with a resultant high or low yield, is accom- 

 panied by a certain relation of percentages of nitrogen, 

 phosphorus and potassium present in the tissues is 

 one thing. To explain the physiological events in which 

 these nutrients participate is another. Even for a 

 practical purpose the utilization of nitrogen, phos- 

 phorus, potassium and other inorganic nutrients should 

 be evaluated in relation to climatic and physiological 

 factors influencing the organic metabolism of the 

 plant. Assuming that a given climatic complex is 

 operating, there are interrelations among nutrient ele- 

 ments that may be studied with profit, as one phase 

 of the development of knowledge of plant nutrition. 

 The interrelations of nitrogen and potassium have 

 been given special attention. The quantitative im- 

 portance of these two elements provides one reason 

 for this. 



The form of nitrogen supplied to the plant, whether 

 as nitrate or ammonia, seems to influence the time at 

 which potassium deficiency injury appears, when the 

 availability of this element is in a range of deficient 

 supplying power on the part of the medium. This 

 has been explained by the theory that potassium is 

 in some way essential to nitrogen transformations in 

 plant metabolism. When potassium is deficient in 

 the root medium and if ammonia enters the plant 

 rapidly, the synthesis of some forms of organic nitro- 

 gen may fail and ammonia accumulate, with the pro- 

 duction of severe and rapid injury to the tissues, as 

 illustrated by experiments on tomato plants (Wall, 

 1940). High nitrogen in nitrate form may accelerate 

 the injury produced when the potassium supply is 

 deficient, within certain zones of deficiency, according 

 to some observers. The whole question of nitrate and 



