PLANTS USED TO ENRICH SOIL. 17 



PLANTS USED TO ENRICH S 



During the year, rain falls on the land leeching 

 out much soluble fertilizer, unless there be some way 

 of holding it in the soil. Fertilizer must be in a solu- 

 ble condition before plants can appropriate it. Xow, 

 if there are no plants present to appropriate this solu- 

 ble fertilizer, it is plain that the rain will carry this 

 portion out of the soil into the water-ways ; but if 

 plants use it at once, when it becomes available, it re- 

 mains on the land. When these plants decay, they re- 

 turn this stored up food and humus to the soil. 



PLANTS AS A SOURCE OF NITROGEN. 



The source of nitrogen, primarily, is the air ; it en- 

 ters the plants in different ways 5 some take it up from 

 the soil, and a few are known to take it from the air 

 directly. Plants that do not appropriate it from the 

 air are still important conservators of nitrogen, in 

 that they take it up from the soil and keep it from 

 wasting, and at the end of their life they give it back. 

 This class of plants cannot give to the soil more nitro- 

 gen than they draw out, but they can conserve it for 

 future plants. Besides this, they pile up the other 

 soluble elements of plant-food. The nitrogen-assimi- 

 lating plants store up varying amounts of this element 

 and give it to the soil, thus actually adding to the sup- 

 ply of this important element and keeping the other 

 elements from wasting. By producing a crop on land 

 for a number of years, and utilizing it carefully, the 

 land becomes richer until finally it will grow full 

 crops. 



The best plants for green manuring or soiling now 

 in cultivation in the South are cow-peas (Dolichos sp.) 



