The Nitrogen Problem in Crop Production. Ill 
require organic matter (/.«., decayed plant remains) for food 
their action is best seen on land where vegetation is left 
to die back. Land which has gone out of cultivation and is 
left to cover itself with weeds, grasses, &c., or to -become 
permanent pasture, no matter how poor, will steadily enrich 
itself in nitrogen so long as calcium carbonate is present. A 
Rothamsted plot left to run wild is gaining something like 
100 lb. of nitrogen per acre in the top 9 inches every year ; 
indeed, there is reason to suppose that soil came by its 
original stock of nitrogen compounds through the action of 
these organisms. The conditions in arable land are less 
favourable to their action, and at present it is not clear 
that these unattached nitrogen-fixing organisms play any great 
part in ordinary farm practice. 
The Losses of Nitrogen on the Farm. 
We now turn to the other side of the account to see in 
what ways nitrogen is lost, and how the losses may be kept 
low. The two most serious are : (a) drainage ; ( b ) bacterial 
action. 
Loss by drainage. — The ready solubility of nitrates is an 
advantage so long as a crop is on the ground to take them, but 
a disadvantage under other circumstances, since it leads to 
their being washed away. The loss thus suffered during the 
year cannot be estimated precisely, but a few examples will 
give an idea of its amount. A piece of ground at Rothamsted 
kept clear of crops and weeds loses by drainage 31’4 lb. of 
nitrogen each year, equivalent to 188 lb. of nitrate of soda, 
worth about 17s. 1 One of the wheat plots receives sulphate of 
ammonia every other year, but its effect shows in the first year 
only, and none is left for the second year. It is well known 
that a wet autumn and winter act unfavourably on the wheat 
crop ; indeed, Dr. Mill has shown that there is almost a mathe- 
matical relationship between rainfall and yield. One very 
important reason is that in a wet winter the nitrates are much 
more completely washed out of the soil than in a dry one. 
Again, it is often noticed on light sandy or gravelly soils that 
where a rick has stood in a field throughout the winter, the 
crop subsequently obtained does better than on the rest of the 
field which stood bare. The explanation is mainly that the 
rick kept off the rain and prevented nitrates from being 
washed away. 
There are two ways of reducing the loss: (1) to use well- 
balanced manures during the rotation, so that the preceding 
1 Warington estimated the loss from soil continuously growing wheat at 
about one quarter this amount. 
