FERTILIZERS FOR ROOT CROPS 223 



Flax and spring wheat are much alike in food require- 

 ments. 



301. Potatoes.* Potatoes are surface feeders and 

 when grown continually upon the same soil without 

 manure, the yield per acre decreases more rapidly than 

 that of any other farm crop. Experiments with pota- 

 toes by Lawes and Gilbert, using different manures, 

 gave the following result : ?8 



AVERAGE YIELD PER ACRE FOR 12 YEARS. 



Tons. Cwt. 



No manure i 19! 



Superphosphate 3 5 



Minerals alone 3 yf 



Nitrate of soda alone 2 4f 



Mixed manures and nitrogen 5 17! 



Farm manures, alternate years 4 3! 



Potatoes require liberal general manuring re-enforced^ 

 with wood ashes or other potash fertilizer. In the 

 rotation they should follow grain or pasture land, pro- 

 vided the fertility of the soil is kept up. 



302. Sugar-Beets. This crop is more exacting in 

 its food requirements than any other root crop. Ex- 

 cessive fertility is not conducive to a high content of 

 sugar. Soils in a medium state of fertility usually 

 give the best results. 79 Sugar-beets should not receive 

 heavy dressings of stable manure, because an abnor- 

 mal growth results. Nitrogenous fertilizers can be 

 applied only in limited amounts, heavier dressings of 

 potash and phosphoric acid are more admissible. 

 When sugar-beets follow corn which has been manured, 

 or grain which has left the soil in an .average state of 

 fertility, the food requirements are well met. 



