The Food of our Agricultural Crops. 
83 
decide the question one way or the other. It is very fortunate 
that so large an area in our various experimental fields has 
been kept free from all nitrogen in manures, and, had we known 
that land which had become " clover-sick " would grow other 
leguminous plants perfectly well, we should not have wasted 
twenty years in the hopeless attempt to grow clover, and we 
should have been in advance of our present position by the 
same period. 
At the beginning of this paper I made a few remarks upon 
the position of agricultural science at the time of the publica- 
tion of the first number of this Journal. Mr. Rham, in his prize 
essay, considered humus to Le the chief source of fertility in 
soils ; it is quite as much so now as it was then. He also said it 
was a complex substance, which should occupy the attention of 
chemists ; and it has been the subject of investigations by them. 
It may now be desirable to pass in review, very shortly, the 
knowledge we have acquired regarding the food of our agri- 
cultural crops. Humus (in which term I include all vegetable 
matter in a certain state of decay) is very insoluble in water ; 
but sooner or later, it assumes the form of nitric acid, which 
combines with lime or other alkaline substances in the soil, and 
then becomes very soluble in water. These compounds rise 
and fall with the water in the soil, coming to the surface in dry 
weather, and passing into the drains, in the absence of growing 
vegetation, in wet weather. When a crop is in the full vigour of 
growth, the soil-water may contain no nitrates, the crop having 
taken them all up; but at all other times the soil-water con- 
tains more or less nitrates. Being soluble in water, and entering 
into no combination with the soil, nitrates cannot accumulate. 
Each year fresh nitrates are formed from the decomposition of 
the humus, the fertility of land depending largely upon the 
amount of nitric acid liberated every year. What we call " con- 
dition," is so much added to the stock of organic matter, which 
in the course of a few years is decomposed, yielding nitric acid 
and mineral substances. 
It appears probable that our grain and root crops take up 
the greater portion, or, perhaps, the whole of their nitrogen, in 
the foi'm of nitrates, and, provided the necessary mineral food is 
in the soil, the growth of these crops depends upon the amount 
of nitric acid which is available. The great value placed upon 
nitrate of soda as a manure for corn crops is a sufficient proof 
that the necessary amount of mineral food exists in the soil. 
The main object of agriculture is to produce crops which yield 
large quantities of starch or sugar. In Great Britain, wheat, 
barley, oats, and potatoes yield the starch, and the root crops 
g 2 
