MAINTAINING SOIL FERTILITY 3 1 



selected that will tend to keep down weeds. Cultivated crops 

 should be included with those that are sown broadcast. 



2. Legumes are Profitable. — By including legumes as clovers, 

 Canada field pea, cowpea, velvet bean, soy bean, etc., in a rotation, 

 it is possible to gather considerable nitrogen, which is the most 

 expensive fertilizing element to buy, from the air. A crop of 

 red clover, one year old, is estimated to contain 20 to 30 pounds 

 of nitrogen in the roots, per acre. A crop of cowpeas in Louis- 

 iana furnishes 100 pounds of nitrogen per acre. By plowing 

 under leguminous crops enough nitrogen is often furnished so 

 that the following crop does not require any extra supply, and 

 if some "nitrogen has to be supplied, that amount is much less 

 than it would be were not nitrogen gathering crops utilized. 



The Minnesota Experiment Station^ found a loss of 2,000 

 pounds of nitrogen per acre when wheat, barley, corn and oats 

 were grown for twelve consecutive years ; two-thirds to three- 

 fourths of this amount was not used by the crops but was lost 

 in other ways. The Ohio Experiment station^ found that there 

 was a gain of 300 pounds of nitrogen per acre in excess of what 

 the crop utilized when clover was included in five-year rotations, 

 covering periods of ten years. When timothy and non-legumes 

 were used in place of clover, nitrogen was lost from the soil ; 

 the loss of nitrogen from the soil was a little more than that 

 removed by the crop. 



3. The Distribution of Farm Labor. — One of the most important 

 points in favor of a rotation of crops is that it allows of a more 

 even distribution of farm labor. When several crops are grown 

 every year the farmer is able to employ help the greater part 

 of the year and thus secure more efficient labor at a less cost for 

 the work performed than should single crop farming be in 

 vogue. 



4. The Checking or Eradication of Insects and Plant Diseases. — 

 Many times crops become so badly attacked by insects, or in- 

 fested with plant diseases, that there are no profits and often 

 large losses in trying to produce them on the same field con- 



1 Bui. 89. 

 ' Bui. no. 



