112 The Nitrogen Problem in Crop Production. 
crop may take up a large amount of the nitrates present ;.(2) 
to leave the land uncropped as little as possible consistent with 
good tillage. 
The first method is applicable everywhere. As an instance 
of its effectiveness the following result from the Broadbalk 
Wheat Field may be quoted : — 
Crop 
Nitrate in draining water 
running away during 
autumn 
Grain 
Straw 
Badly balanced manure (nitro- 
Bushels 
Cwt. 
gen only). (Plot 10). 
Better balanced manure (nitro- 
gen, potash, phosphoric acid). 
160 
1475 
17-8 parts of nitrogen 
per million of water. 
(Plot 13) 
26-7 
30-75 
8 - 5 parts of nitrogen 
per million of water. 
Much less nitrate is lost from plot 13, where a well-balanced 
manure has been used ; indeed, analysis shows that the top 
9 inches of soil contains about 300 lb. more nitrogen per acre 
than that of plot 10, in spite of the larger amount withdrawn 
by the crop. 
The second method is of more limited application, because 
certain soils must lie uncropped during autumn and winter in 
order to clean the land and get a tilth. Instances are furnished 
by catch cropping, “ bastard,” or “ rag ” fallowing, and sowing 
seeds with corn. The crop will, during the late autumn and 
winter, take up nitrates which would otherwise be washed 
away. In an experiment by Deherain the drainage water from 
soil cropped with wheat alone carried away 28| lb. of nitrogen 
in the form of nitrates per acre during the year, but from soil 
cropped with wheat followed by vetches the loss was reduced 
to less than 13 lb. per acre. 
Loss by bacterial action. — (a) Certain bacteria decompose 
nitrates with liberation of the nitrogen as gas or production of 
an injurious “ nitrite.” This change only goes on in the 
absence of air, and there is no evidence that it takes place 
under conditions obtaining in British agriculture. It happens, 
however, in the swampy “ paddy ” soils of the East, and 
renders the use of nitrate of soda unprofitable there. 
( b ) Other bacteria live on nitrates and ammonia, which are 
thus temporarily withdrawn from the reach of the plant roots ; 
when these bacteria decay some of their nitrogenous con- 
stituents may be reconverted into plant food. Not sufficient 
is known about this source of loss to say anything as to its 
practical significance. 
