200 SCIENTIFIC AGRICULTURE. 



yard manure is not subject to any special law, but is to be used 

 according* to its quality and condition, and adapted to circum- 

 stances. Vegetable substances are all similar in their nature 

 and operation, and are modified by conditions and circum- 

 stances. They are all subject to the same laws, and their 

 relative value depends on their constitution and adaptation to 

 each particular case. 



GREEN MANURES. 



By green manures, is understood those plants which are 

 grown for the purpose of being ploughed in and mixed with the 

 soil before being harvested or used as food for animals. This 

 plan of manuring is by no means of recent origin ; it was 

 known and practiced among the Romans. The plants most in 

 use for this purpose in the United States are red clover, buck- 

 wheat and grass in the form of green sward. Several other 

 plants are used in Europe, viz., rape, lupine, vetches, rye, tur- 

 nip, carrot and beet tops, borage, spurry, sea weeds and fresh 

 water plants. 



The advantages of green manures, according to Johnston, 

 are, 1. They undergo decomposition sooner than dry vegeta- 

 ble matter, and consequently become sooner available for the 

 food of succeeding crops. 2. The nitrogen and carbon which 

 they contain, if allowed to decay in the open air, are lost ; 

 while if the plants had been buried, before decay, these gases 

 would have been mostly retained in the soil for the use of suc- 

 ceeding crops. 3. By ploughing in a crop of plants, the or- 

 ganic matter is more equally distributed through the soil than 

 could be done by any other means. 4. Green manures are 

 available where other manures are scarce, and in soils deficient 

 in organic matter. 5. The plants used as green manures, bring- 

 up towards the surface by their roots, matters which had sunk 

 into the soil too deep to be of much service. 6. It restores to 

 the soil all it took from it, in a more soluble and available con- 



