1 88 THE FIRST BOOK OF FARMING 



phosphoric acid and 110.56 pounds of potash." 

 Farmer's Bulletin, 16 U. S. Dept. of Agriculture. 



" It is now grown in all the States south of the 

 Ohio River, and in 1899 there were planted nearly 

 800,000 acres to the crop. Basing our estimate on 

 the amount of nitrogen stored in the soil by this 

 crop, it is fair to say that fully fifteen million pounds 

 of this valuable substance were collected and re- 

 tained as a result of the planting of the cowpea 

 alone. This at fifteen cents per pound (the market 

 price of nitrogen) would be worth something more 

 than $2,000,000 for nitrogen alone." Year Book of 

 the Department of Agriculture, 1902. 



The Clovers. These are the most extensively 

 grown plants for green manure purposes in the 

 United States. They are deep-rooted, and are able 

 to use mineral food that is too tough for other 

 plants. They furnish large crops of hay or green 

 forage and a good aftermath and sod to turn under 

 as green manure, or the entire crop may be plowed 

 under. 



Red Clover is the most widely planted (Fig. 80). 

 It is a perennial plant and grows from the most 

 northern States to the northern border of the Gulf 

 States. It grows best on the loams and heavier 

 soils well supplied with water, but not wet. It is 

 sown broadcast at the rate of from ten to twenty 

 pounds of seed per acre. In the North it is gen- 

 erally sown in the spring on fields of winter grain. 

 In the South, September and October are recom- 

 mended as the proper sowing times. It is the cus- 



