120 BOARD OF AGEICULTURE. 



soil are frequently cited as a strong argument in favor of the 

 opinion entertained by some leading agricultnral chemists 

 ( Wolif) , namely, that its fnnctions as a nitrogen source for the 

 roots are altogether of a secondary importance. 



Whatever way fnture inquiries may decide regarding this 

 assumption, it is evident that the ordinary amount of ammonia 

 in the soil, as previously stated, cannot secure the largest 

 possible yield of farm crops. 



Dr. Hellriegel, who since 1863 has been engaged with ex- 

 periments concerning the question. How much of the various 

 articles are needed to secure the highest possible yield of 

 some of our prominent farm crops ? found that the smallest 

 amount of nitrogen required to secure the highest yield, tak- 

 ing, of course, all other requirements equally favorable, 

 amounts in the case of wheat to seventy-three (73) pounds of 

 convertible nitrogen for every one million pounds of earth ; 

 for rye, sixty-three pounds ; for oats, fifty-six pounds, con- 

 sequently, under even favorable conditions, at least many 

 times as much as the soil, in the form of ammonia, ordinarily 

 contains. 



The second form in which the convertible nitrogen occurs 

 in the soil, consists in the nitric acid. This acid is derived 

 periodically, as Ave have seen, from the air by means of rain- 

 fall, dew or snow-fall, and also from the oxidation of the 

 ammonia under the influence of basic oxides, like lime, etc. 

 Its main quantity, however, depends on the disintegration, 

 and subsequent oxidation of the animal and vegetable matter 

 stored up in the soil. As the process of their oxidation 

 requires a full access of the air, we notice the formation of 

 nitric acid particularly in the surface portion of the soil, the 

 compost heap, and even the manure pile. 



The nitric acid forms very soluble compounds with every 

 basic article of plant-food ; it passes, comparatively speaking, 

 quite rapidl}^ to the subsoil, and forms, in combination with 

 lime and magnesia, a normal constituent of the drainage 

 waters of cultivated lands. 



It is here of interest to notice, that ammonia and nitric 

 acid behave quite differently towards the soil ; for the former 

 is retained, as we have seen, in the surface soil, whilst the 

 latter passes by the aid of percolating waters to the lower 



