The Sottrces of the Nitrogen of our Leguminous Crops. 701 
In the second into hay. The land is thus occupied for two 
.-ears, and the assumption is, that in this way highly nitrogenous 
:rops will be obtained with mineral but without any nitrogenous 
manure, and that the land will be left in high condition so far 
as nitrogen is concerned for the growth of saleable crops, such 
jfts potatoes, or grain, which require nitrogenous manuring. In 
other Avords, the plan is, as he puts it, first to grow nitrogen- 
|accu:ivalating crops for home consumption, and afterwards 
initrogen-consuming crops for sale. The experiment has been 
jin progress too short a time to judge how far it will be success- 
ful in a series of years, or of rotations. It is at any rate pretty 
certain that, to obtain luxuriant leguminous crops so frequently 
as the plan supposes, it will be necessary that the description 
I of plant grown should be varied from time to time. It 
has also yet to be determined to what extent the nitrogen 
j removed in the leguminous crops and made into silage or hay 
must be returned to the land in the form of manure, or whether 
I part of the green crop itself should be ploughed in, for the after- 
, growth of the saleable crops. 
There is, of course, nothing new in the fact that, after the 
growth of a leguminous crop, such as red clover for example, 
, the soil is left in a higher condition for the subsequent growth 
of a grain crop ; and that, in fact, the growth of such a legu- 
minous crop is to a great extent equivalent to the application 
of a nitrogenous manure for the cereal. Indeed, history tells 
us that more than two thousand }ears ago it was recognised 
by the Romans that the occasional growth of plants of the 
leguminous family had the effect of increasing the growth of 
the gramineous crops with which they were alternated, and it 
was stated that the effect was equival'?nt to that of applvinc 
manure. Thus Varro says that, " Certain things are to be 
sown, not with the hope of any immediate profit being derived 
from them, but with a view to the following year, because, 
being ploughed in and then left in the ground, they render the 
soil afterwards more fruitful ; " and the plants used for this 
purpose were lupins, beans, vetches, and other legumes. 
Now, however, that the character of the action is more 
clearly understood, and it is certain that there is actual gain 
of nitrogen from sources external to the soil itself, it seems 
desirable that at any rate tentative trials should be made on 
different descriptions of soil, with the view of ascertaining 
whether more advantage cannot be taken of this source of nitro- 
gen than our established practices of rotation at present secure. 
The experimental results which have been brought forward 
clearly establish that there is great gain of nitrogen under 
