270 REPORT—1905. 
the table will be seen the comparative value of these residues in the case 
of lucerne and red clover, 
Taste II, 
Grain Total Produce 
Harvest ies * oF = Par 
After Red After Red 
After Lucerne Mover After Lucerne Glover 
Bushels Bushels lb. lb. 
1899 39°3 43°0 8,108 8,505 
1900 28:9 191 4,564 2,992 
1901 27-0 21°4 4,054 3,185 
1902 201 ii 3,553 3,025 
1903 19-9 16°7 3,035 2,528 
Total.» A 1352 117°9 23,304 20,233 
As we have previously seen how great the benefit of a single year’s 
growth of red clover may be on the succeeding crops, an idea can be 
formed from the comparison in the latter table of how much more lucerne 
may contribute towards building up a fertile soil ; a point which was very 
markedly brought out in the experiments of the late Mr. James Mason. 
The question of the fixation of atmospheric nitrogen by bacterial 
agencies does not, however, end with the organisms living symbiotically 
on the leguminous plants, for several other organisms have latterly been 
discovered which possess the power of fixing nitrogen independently, 
provided they are supplied with the necessary nutriment. Of late atten- 
tion has been chiefly directed to a conspicuous organism known as 
Azotobacter chroococewm, which may be readily identified in most cultivated 
soils. The impure cultures (which may be quickly obtained by introducing 
a trace of soil into a medium containing no nitrogen, but a little phosphate 
and other nutrient salts, together with one or two per cent. of mannite 
or other carbohydrate) fix nitrogen with considerable activity ; in one 
case, for example, when working with a Rothamsted soil, as much as 
19 mg. of nitrogen were fixed for each gram of mannite employed and 
partially oxidised. But Beyerinck, the discoverer of the organism, now 
attributes the nitrogen fixation to certain other organisms which live 
practically in symbiosis with the Azotobacter, and which are present in 
the impure cultures just referred to. The exact source of the nitrogen 
fixation may be left a little doubtful ; still the main fact remains that 
from the bacteria present in many soils one or a group may be found 
capable of effecting rapid and considerable nitrogen fixation if the necessary 
conditions, chiefly those of carbohydrate supply, are satisfied. 
But how is the carbohydrate supply to be obtained? Under the 
normal conditions of arable land farming there are few possibilities in this 
direction, the occasional ploughing under of a green crop being the only 
considerable addition of organic matter, other than manure, which is 
possible in practice. As a matter of experience the plots at Rothamsted, 
which have been growing crops without manure continuously for the last 
fifty years, indicate but little gain of nitrogen from the atmosphere. 
After a rapid fall in production for the first few years, the yield has 
become so nearly stationary that any further decline is not as yet dis- 
cernible amid the fluctuations due to season. 
