322 BOARD OF AGRICULTURE. [Pub. Doc. 



stituents. 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 succeeding 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 neces- 

 sary to the best conditions 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 pro- 

 duction 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 car- 

 bonic acid. This acid helps to keep the soil chemically 

 active, i. e., 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, helping 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 fermentation which exert a beneficial in- 

 fluence upon the soil. These processes are favored by the 

 shade furnished by the crop, by the restricted circulation of 

 the air and by the more uniform soil temperature which the 

 occupying of the land by a crop secures. The incorporation 

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



