GREEN MANURING 133 
into available plant food and lost, while nothing takes its place. 
For these reasons the practice of fallowing has been almost wholly 
given up, except under semi-arid conditions. Indeed, it is a 
growing custom not to allow the soil to remain fallow at all, not 
even during the season of the year when the main crop is not 
growing; but to sow it with a cover crop, which will catch and hold 
the plant foods that are constantly being made available. Nitri- 
fication, as we have seen, goes on at all seasons when the soil is 
not actually frozen, and considerable losses of nitrogen will result 
from the leaching of these nitrates away from the soil at the seasons 
when it is not covered with a crop. The loss may be largely 
retained by a quickly growing cover crop. Such cover crops 
plowed into the soil will benefit it, and the next main crop will be 
improved; but a fallow season leads to direct loss. 
GREEN MANURING 
The use of cover crops, just mentioned, is closely related to the 
practice of green manuring, but the latter has an additional pur- 
pose besides all the advantages of a cover crop. It not only pre- 
vents the loss of available plant foods by drainage, but it also 
adds a considerable quantity of food to the soil. It not only 
serves as a catch crop to hold the nitrates that may form during 
the season when the main crop is not growing, but it may add to 
the total nitrogen of the soil. The general plan of green manur- 
ing is to grow upon the soil some leguminous crop that increases 
the nitrogen content of the soil, and, after proper growth, to 
plow the whole crop into the soil. The addition of this large 
amount of organic matter to the soil will stimulate the bacterial 
activities of decomposition. The roots, stems, leaves, and fruits 
of the crop undergo a decomposition and subsequent nitrifica- 
tion, resulting finally in the formation of nitrates which can be 
utilized by the next crop grown on the same soil. 
When adopting the plan of green manuring the first thing is to 
select the crop that is to be utilized. Manifestly, from what has 
