460 Mineral Nutrition of Plants 



The outstanding factor affecting the nitrogen level is tissue moisture. 

 Age is also dominant. In fact, after a crop is in its second year of growth, 

 it is difficult to affect the nitrogen level by application of fertilizer. 



Minimum temperatures exert a strongly negative influence while 

 maximum temperatures exert a weaker positive influence. Soil moisture 

 is also negative but its influence is weak. Light does not seem to affect 

 the nitrogen level. 



TABLE VI 

 Partial Regressions of Certain Factors on Leaf Nitrogen 



(» = 1373) 



It is evident from our analysis so far that the elements of weather 

 have an overwhelming influence on the growth of sugar cane. When 

 the physiological status of a crop can be controlled by maintaining the 

 moisture and carbohydrate levels at known levels for each stage of 

 growth, it is apparent that the yields which are obtained should be 

 maximal for a particular location and should be related, not so much 

 to the so-called fertility of the soil but to the energy level of the atmos- 

 phere as composed of radiant and heat energy. To be sure, we can hope 

 to produce the maximum crop only occasionally, since every storm, every 

 unfavorable circumstance of soil, weed control, or general mismanage- 

 ment of a crop will reduce the likelihood of the maximum achievement 

 by amounts in direct proportion to the sum total of mishaps. We ought, 

 however, to be able to predict what can be achieved in any given area 

 and proceed from this to narrowing the differences between the actual 

 and the theoretical yields. 



