118 BOARD OF AGRICULTURE. 



The recognition of this fact is, however, modified by the 

 statement, also experimentally established, that the air alone 

 cannot supply, even under the most favorable circumstances, 

 a sufficient amount of nitrogen plant-food to secure a maxi- 

 nmm yield of many of our farm crops. 



Intensive farming, even in case of a most favorable rota- 

 tion, recpiires, as Boussingault has demonstrated, an additional 

 supply of nitrogen plant-food. Hellriegel, who experimented 

 with a richly foliated lupine, noticed that in case the plants 

 were raised in a soil entirely free from any nitrogen com- 

 pounds, yet abundantly supplied with suitable mineral plant- 

 food, only one twenty-fourth part of the organic matter was 

 produced as compared with cases in which a suitable nitrogen 

 plant-food had been added. Clover gained more. He also 

 confirmed again the earlier observation of Wolfl'and others, 

 that the air is a far more efficient source of carbonic acid for 

 plant-growth than of nitrogen. 



Taking even for granted that the available annual supply of 

 nitrogen compounds of the air should be considered, as far as 

 their entire quantity is concerned, equal to the amount required 

 for a good crop, there remain still strong doubts, whether the 

 available supply would be sufficient to meet the periodical 

 demands of the plants. 



The efficiency of any article of plant-food, considering all 

 other circumstances equally favorable, does not so much de- 

 pend on a sufficient quantity to meet the requirements of the 

 entire period of growth, but to furnish enough for the periodi- 

 cal individual wants of the plants under cultivation. 



Different plants behave differently, regarding the amount of 

 nitrogen they need during their various periods of growth. 



Scheven found that in the case of barley, taking its entire 

 amount of nitrogen, in its perfectly ripened state, equal to 

 100; — 1.4 per cent, of nitrogen had been absorbed daily, 

 during its first stage of growth; 2.4 per cent, per day until 

 its blooming; 0.27 per cent, daily, during the first period of 

 the ripening of the seeds, and but 0.15 per cent, afterwards, 

 until perfect ripeness. 



Dietrich, on the other hand, found in the case of the clover, 

 that G.O per cent, of the entire nitrogen of the per ectly 

 ripened plants are absorbed until the stems are growing, 



