14 FARM CROPS 



practical importance to the cultivator of the ^ soil. 

 This, then, opens to us an easy way of maintaining 

 soil fertility. 



In a soil of ordinary fertility, by a proper rotation 

 of crops in which clover or cowpeas or some other 

 leguminous plant occurs, we are continually adding 

 to the soil this valuable and costly element, nitro- 

 gen. Practical experience has taught us that the 

 fertility of the soil, so far as nitrogen is concerned, 

 may be maintained by growing a sufficient number 

 of crops of clover or cowpeas. How, then, is the 

 supply of phosphoric acid related to the growing of 

 leguminous plants? 



The roots of the leguminous plants grow deep 

 in the soil. The roots of our ordinary grain crops 

 are surface feeders, and a soil may soon become 

 exhausted, so far as the plant food available for 

 wheat or corn or potatoes is concerned, and may 

 still be fertile for the growth of clover or alfalfa 

 or cowpeas for the reason that these legumes go 

 deeper in the soil and are able to feed upon plant 

 food there out of the reach of many other crops. 

 When clover or cowpeas or alfalfa is grown for 

 fertilizing purposes, it also brings this potash and 

 phosphoric acid from the deeper layers of the soil 

 to the surface. Not only is soil fertility brought 

 up from the deeper soil, but the roots of plants 

 growing in contact with the soil are continually 

 dissolving the elements of plant food, particularly 

 potash and phosphoric acid, and any crop grown 

 upon the soil for the purpose of green manuring is 

 at the same time increasing the available plant food 

 in the soil by dissolving the unavailable compounds. 



These are some of the reasons why the growth 

 of the leguminous plants on the soil will increase 



