THE SOIL AND ITS IMPROVEMENT 87 



grow through the latter part of the season, on mild days dur- 

 ing ■winter and in very early spring before the soil is in condi- 

 tion for tillage for garden crops. Thus time, which would 

 otherwise be of no use in the growth of most garden crops, is 

 used for the production of green manure to enrich the soil. 



If the green manures are composed partly or wholly of 

 plants of the legume family, they will gather nitrogen from the 

 air and add it to the soil as they decay. Winter vetch and 

 crimson clover (Fig. 56) are suitable annual legumes for use 

 throughout the winter. Winter grains, such as rye and wheat, 

 are also used abundantly as green manures, but these do not 

 have the power of gathering nitrogen from the air. As green 

 manures decay they not only add humus, but they add con- 

 siderable plant-food which has been unlocked from the soil by 

 their own grovrth. The decay of green manures in soil is so 

 rapid in warm weather that the plant-food they contain is 

 liberated very soon. In the school garden work, after early 

 garden crops are grown, summer crops may be sown to be used 

 later as green manures. Suitable legumes for this purpose 

 are cowpeas and soybeans. If these are sown about the first 

 or middle of June, in the latitude of 'New York or Philadel- 

 phia, they will thrive and gather large quantities of nitrogen 

 with which to enrich the soil for future garden crops. 



In localities where stable manure is difficult to obtain, green 

 manures should be grown regularly, either through the winter 

 season or during midsummer for the improvement of soils. 



Cover crops, or green crops grown during the winter are 

 beneficial in a number of ways. (1) They serve the purposes 

 of green manures. (2) They prevent the leaching or waste 

 of plant- food during the winter season. (3) They retard the 

 washing away of surface particles of soils. (4) They help to 

 cause rainfall to enter the soil more readily. (5) Their roots 

 allow the entrance of air, thus causing soils to dry more 

 quickly for early spring gardening. (6) They prevent the 

 blowing of soils.. 



