COVER CROPS 85 



family) have this characteristic of appropriating 

 nitrogen from the atmosphere. Under proper man- 

 agement practically all of this nitrogen collected 

 by a cover crop becomes eventually available for the 

 fruit trees. In spite of scientific investigations there 

 is still a great deal of question as to how much nitro- 

 gen any particular crop actually secures from the 

 air. It is easy, of course, to analyze cowpeas or clover 

 plants and determine the amount of nitrogen con- 

 tained; multiply this by the amount of growth in 

 tons to the acre, and say that the crop contains so 

 much nitrogen. The fact is, however, that only a 

 part of this nitrogen really comes from the atmos- 

 phere, the balance being taken from the soil. In 

 a great many cases the amount taken from the at- 

 mosphere is small or insignificant. 



Most of the leguminous crops do not form the 

 necessary nodules to begin the bacterial action re- 

 quired for nitrogen assimilation until the soil has 

 been inoculated with the appropriate bacteria. This 

 inoculation conies about naturally, though slowly, 

 after a" time, but in many cases practical growers 

 have found it desirable to use artificial inoculation. 

 This is best accomplished by the distribution of 

 inoculated soil over the orchard tract. For example, 

 if one is to grow soy beans on land where they have 

 never been grown before, he should commence by 

 sowing a small amount of soil secured from a field 

 where soy beans have been established for some 

 time. By this means the necessary bacteria are in- 

 troduced and the soy beans thrive from the start and 

 (what is more important) are able to assimilate con- 

 siderable quantities of atmospheric nitrogen. In 

 actual practice too much faith is placed in the legu- 

 minous crop as such, and not enough attention is 

 paid to bringing the cover crop up to its highest 



