GREEN MANURING. 123 
where water is scarce and must be conserved, fallowing may result 
in advantage. It is also claimed that fallowing may enable the 
soil to dispose of the poisonous secretion from plants that would 
injure a second crop growing on the same soil. But, apart from 
these facts, fallowing results in a loss to the soil. In the first place, 
fallowing adds nothing to the soil, while a crop, especially a legume, 
may do so. Moreover, during the fallow season the bacterial activi- 
ties in the soil continue, converting the material in the humus 
into nitrates and other soluble substances, which are then available 
plant foods. If a crop is growing in the soil these will be absorbed 
by the crop and utilized. If, however, the land is fallow, there is 
nothing to utilize these products as they are formed, and they will 
be, in a measure, lost; for they will be dissolved in the soil waters 
and drained away from the soil into the general system of brooks and 
streams. If, in the meantime, nothing of any value is added to 
the soil, at the end of the fallowing it will actually be poorer than at 
the beginning, except in the matter of water. Its store of humus 
will be partly converted 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 for special soils. 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. Nitrifica- 
tion, 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 purpose 
