MAINTAINING SOIL I'KRTILITV 33 



their crops in paying the merchant for the last year's supplies. 

 They often live from year to year on the credit basis and pay 

 much more for their supplies than the farmer who is able to 

 pay for what he gets in cash. In certain sections of this coun- 

 try this credit system of farming has proved disastrous because 

 one or two bad years caused the loss of the farm. The single- 

 crop farmer generally has to buy more supplies than the farmer 

 who grows several crops. The farmer who practices rotation 

 has crops to sell at different times in the year and so has a 

 more regular income than the single crop farmer who gets his 

 money but once a year. 



7. Preventing Losses of Fertility. — The farmer who rotates his 

 crops may sell the crop that removes the least fertility from the 

 soil and if the money crops remove a great deal of fertility, 

 he may regulate his rotation so as to restore this loss cheaply. 



8. A rotation of crops utilizes plant food more evenly than when 

 single crops are continually grown. Corn, wheat and other grain 

 crops use a great deal of nitrogen and phosphoric acid while 

 tobacco and potatoes are heavy potash feeders. By the proper 

 selection of crops forming rotation, the plant food may be drawn 

 on more evenly and losses of fertility prevented through leach- 

 ing, etc. 



9. Deep and Shallow Rooted Plants. — A rotation of crops has 

 an advantage over single crop farming because of the variation 

 in depth of root systems of different crops. Alfalfa and corn 

 have deep tap roots and obtain food from the subsoil, while 

 oats, timothy, blue grass, rye, etc., have shallow roots and feed 

 from the upper soil. By alternating deep and shallow rooted 

 plants the fertility from the subsoil and surface soil is more 

 evenly utilized. Often the surface soil may predominate in ni- 

 trogen and phosphoric acid and the subsoil in potash and lime. 

 When the fertility is thus distributed the alternating of shallow 

 and deep rooted plants is important as the fertility of the subsoil 

 is brought to the surface soil by the decay of roots. 



Another advantage of growing deep and shallow rooted plants 

 is the improvement of the physical condition of the soil. Deep 

 rooted plants tend to make a soil more porous because the de- 



