The Nitrogen Problem in Crop Production. 105 
purchased manures, and the one most liable to waste both 
before and after spreading on the land ; while the nitrogenous 
constituents of food, though not as costly as the oil, are never- 
theless a serious item in the feeding-stuffs bill. 
In the present paper it is proposed to deal only with crop 
production, which is as a rule the most important phase of the 
problem. The bulk of the nitrogenous feeding-stuffs wanted 
by the animal can be grown on the farm, and a large part of 
the nitrogen actually consumed in the food is excreted and 
may pass into the manure. Hence, even for the dairyman 
and the farmer who fattens stock, the nitrogen problem largely 
resolves itself into questions of manure-making and crop 
production. 
It is a matter of common experience that the yield of 
non-leguminous crops on nearly all soils is increased by 
supplying nitrogenous manure. The increase does not go on 
indefinitely, and heavy dressings bring in proportionately less 
return than lighter ones. Up to a certain point the extra crop 
more than pays for the extra manure, but beyond that point 
the increase in yield is so small that it no longer pays for 
itself. It would require a nice calculation of odds to determine 
just how far manuring can profitably go. 
The Sources of Nitrogen available to the Farmer. 
In ordinary circumstances there are four sources of supply 
available. (1) Nitrogen compounds already in the soil ; (2) 
purchased manures ; (3) purchased food-stuffs, the nitrogen of 
which largely passes into the animal excretions ; (4) nitrogen 
of the air fixed by bacteria. 
1. Nitrogen compounds in the soil . — The amount of nitrogen 
present even in very poor soil is surprisingly great, and would 
appear sufficient to last for a large number of crops. The 
figures in Table I. illustrate this point very well. 
Table I. — Amounts of Nitrogen present in certain Soils. 
Percentage 
of nitrogen 
Lb. of 
nitrogen in 
top 9 in. 
per acre 
Number of four- 
quarter wheat 
crops (including 
straw) containing 
this quantity of 
nitrogen 
Rothamsted soil, unmanured for 60 
years ...... 
•097 
2,450 
47 
Barren sandy heaths, Kent and Surrey 
•125 
3,400 
65 
Good arable loams, Kent (mean of 15) 
•180 
4,800 
92 
Kent hop gardens, very rich 
■200 
5,300 
102 
Sandwich marsh soil .... 
•681 
17,200 
331 
