288 



UOAV CKOPS FEED. 



most care, unavoidably remain in a soil from which gro\v« 

 ing vegetation is removed. The regular and great increase 

 of total nitrogen in the vetch plot was certainly due in 

 part to the abundance of leaves that fell from the 

 plants, and covered the surface of the soil. But this ni- 

 trogen, as well as that of the standing crops, must have 

 come from the atmosphere, since the soil exhibited no 

 diminution in its content of this element. 



We have here confirmation of the view that atnmonia^ 

 as naturally supplied^ is of very trifling importance to 

 vegetation, and that, consequently, nitrates are the chief 

 natural means of providing nitrogen for crops. The fact 

 that atmospheric nitrogen becomes a part of the soil and 

 enters speedily into organic and inert combinations, also 

 appears to be sustained by these researches. 



Quantity of Nitrogen needful for illaximum Grain 

 Crops. — Hellriegel has made experiments on the eftects 

 of various quantities of nitrogew (in the form of nitrates) 

 on the yield of cereals. The plants grew in an artificial 

 soil consisting of pure quartz sand, with an admixtni-e of 

 ash-ingredients in such proportions as trial had demon- 

 strated to be appropriate. All tlie conditions of the ex- 

 periments were made as nearly alike as possible, except as 

 regards the amount of nitrogen, which, in a series of eight 

 trials, ranged from nothing to 84 parts per 1,000,000 of soil. 



The subjoined Table contains his results. 



EFFECTS OF VARIOUS PROPORTIONS OF ASSIMILABLE NITROGEN 

 IN THE SOIL. 



