70 The Food of our Agricultural Crops. 
of the present day, have become " household words,"' formed 
no part of the science of agriculture at the time Mr. Pusey 
wrote. 
In accordance with the view generally entertained, Mr. Itham 
considered that the vegetable matter of the soil known by the 
name of humus was the source of its fertility. He says that 
real humus is a very complex substance, and suggests that our 
greatest chemists should make investigations into its nature. 
It was an immense step in advance when Boussingault, who 
was a most accurate chemist as well as a practical farmer, pub- 
lished analyses of the various crops grown upon his farm, and 
discussed the question of the fertility and exhaustion of the soil 
in connection with the export and restoration of detinite chemical 
compounds. Having a considerable area of irrigated meadows 
attached to his farm, he considered that the hay grown on these 
meadows was sufficient to restore the ingredients exported from 
his arable land in corn and animal products, and his employ- 
ment of what we now call artificial manures was confined to the 
application of gypsum to clover. 
After the publication of Liebig's work, an immense number 
of experiments with artificial manures were carried out in this 
country While some people recommended that the exact pro- 
portion of each ingredient exported from the farm in the produce 
should be returned in the artificial manure, others argued that 
only those substances should be returned which analysis of the 
soil proved to be wanting. The great battle, however, was over 
the employment of nitrogen. Being the most costly ingredient 
in an artificial manure, the necessity for its use became a question 
of great agricultural importance. Some contended that, pro- 
vided the land was furnished with the necessary mineral ingre- 
dients, the plant could obtain all the nitrogen it required from 
the atmosphere ; while others asserted that no amount of mineral 
food would prevent the yield from declining unless nitrogen 
in some form was used with the minerals. In an article pub- 
lished in this Journal, Mr. Pusey summed up the conclusions 
derived from innumerable experiments in the following remark : 
" Ammonia for corn, phosphorus for roots," which, although not 
representing any scientific law, furnished in the simplest and 
plainest language a most valuable practical rule for farmers. 
So lit tie was known regarding 1 the relation to the soil of some 
of the -most important ingredients of growth, that, at the sugges- 
tion of an eminent chemist, a patent was taken out for fusing 
phosphate of lime and potash with other substances into a glass, 
to prevent them from being washed out of the soil ; while at 
the same time some one else was bringing chemical action to 
