The Nitrogen Problem in Crop Production. 107 
3. Purchased feeding-stuff's. — Most of the nitrogen of pur- 
chased feeding-stuffs may go to enrich the soil ; only a small 
part — varying from about 30 per cent, in the case of a dairy 
cow to about o per cent, in the case of a fatting bullock — is 
retained by the animal to make milk or meat. The remainder 
is excreted — the most useful part in the urine, and the rest in 
the solid excreta. When the conditions allow of it, there is no 
better method of increasing fertility than to fatten animals on 
the land. Some of the most fertile tracts of the Lower Green- 
sand formation in Surrey and Sussex owe their productiveness 
largely to the practice of buying in sheep in autumn and 
fattening them out during winter and spring on purchased 
concentrated foods. The fertility of some of the very pro- 
ductive marsh and brick earth soils of Kent and Sussex has 
been maintained and often increased by fattening bullocks. 
Nitrogen is thus transferred from the foreign soil, where the 
purchased food was grown, to the home soil, where it is fed to 
animals. The tendency of modern agricultural conditions is 
to enrich some of our own soils at the expense of the soil of 
other countries. 
When animals cannot be fed on the land, but have to be fed 
in stalls, boxes, or yards, the proportion of nitrogen reaching 
the soil is diminished, for dung cannot be made without loss. 
Even if the utmost care is taken, about 15 per cent, of the 
nitrogen is lost, and the loss falls entirely on the quickly 
available, i.e., the most useful, nitrogen compounds. A greater 
loss takes place if the dung cannot be used straightway, but has 
to be stored in a mixen ; indeed, before the dung reaches the 
soil nearly half its nitrogen may have gone even on a well- 
conducted farm. The loss is still greater where the manage- 
ment is bad, e.g., where the dung is made with excessive quan- 
tities of litter, and left exposed to rain in open yards for long 
periods, or where the liquid is allowed to run to waste. 
The amount of nitrogen furnished by the food is propor- 
tional to the amount of protein (or albuminoid) present. Thus 
for certain common foods the order would be : — 1 (supplying 
most nitrogen), decorticated cotton cake ; 2, linseed cake 
containing 7 per cent, oil ; 3, linseed cake containing 10 per 
cent, oil ; 4, undecorticated cotton cake ; 5, pulse ; 6, dried 
brewers’ grains ; 7, wheat offal ; 8, barley, and 9 (supplying 
least nitrogen), maize. It is noteworthy that linseed cake 
containing 7 per cent, of oil makes better manure than the 
grade containing 10 per cent. Wheat offal also stands above 
any corn, whether barley, oats, wheat, or maize. 
4. Nitrogen fixed bg bacteria. — (a) Bacteria associated with 
leguminous crops. — In relation to the nitrogen problem the 
various leguminous crops — peas, beans, clover, sainfoin, lucerne, 
