28 



This loss can be prevented by keeping the soil filled with feeding root- 

 lets of growing pi ants The myriad hungry rootlets will take up the sol- 

 uble nitrogen and it becomes a part of the plant. It is locked up, so to 

 speak, in the vegetable tissues, and will remain so locked up until these 

 tissues decay. 



As has been pointed oiat, the season when this loss is most likely to 

 take place is in the late autumn ; hence, to prevent this loss, or for nitro- 

 gen co7iservalion, those crops are most valuable which are not affected 

 by the autumn frosts and which will continue to grow as late as jjos- 

 sible. Measures to insure nitrogen conservation are self-evidently most 

 important upon the richer soils which are light and porous in character 

 and which have open subsoils. 



Green-manuring cannot increase the store of either phosphoric acid, 

 potash or lime, but it can be made to increase the solubility and there- 

 fore the availability of these soil constituents. The feeding roots of 

 growing plants are furnished with a small amount of acid and this acid 

 takes hold of and makes soluble elements which are not soluble in pure 

 water. The elements so made soluble become a part of the growing 

 crop, and when that crop decays they become available to the suoceed- 

 ing crop, whose labor is therefore lightened because it finds a larger 

 store of available plant food than would have been present had not the 

 green-manuring crop been grown. 



Green-manuring increases the store of humus (partially decayed 

 vegetable matter) in the soil, and humus is necessary to the best con- 

 ditions of fertility and productiveness. It increases the capacity of the 

 soil to retain and conduct water ; it promotes beneficial chemical changes 

 among the different soil constituents ; changes which result in making 

 originally inert soil materials available as food for plants. A suitable 

 amount of humus contributes largely to the production of that physical 

 condition of the soil which makes it possible to bring it into good tilth 

 and to maintain it in that condition, 



The products of the decay of the vegetable matter furnished by green- 

 manuring exert a very beneficial effect upon the soil Among the most 

 important of these products is carbonic acid This acid helps to keep 

 the soil chemically active, i. t\, to produce beneficial chemical changes 

 which result in making more food available. This acid, further, helps 

 largely to dissolve the useful constituents of the soil, especially the lime 

 and phosphates, thus bringing them within the reach of subsequent 

 crops. This acid further attacks the stones and rocks of the soil, help- 

 ing to disintegrate them. This action is especially important in the case 

 of all rocks and stones containing lime. 



The green-manuring crop is useful, further, because while it occupies 

 the land the conditions are more favorable for those processes of fer- 

 mentation which exert a beneficial influence upon the soil. These proc- 

 esses are favored by the shade furnished by the crop, by the restricted 

 circulation of the air and by the more luiiforra soil temperature which 

 the occupying of the land by a crop secures. The incorporation of tlie 

 vegetable matter of the green crop in the soil may be the means of 

 warming it. The darker color resulting from the presence of humus 



