GREEN MANURING. 



I2 3 



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 



