MISCELLANEOUS CROPS 233 



has restricted powers of nitrogen assimilation. 37 Flax 

 does not remove a large amount of fertility but if 

 grown too frequently the tendency is to get the land 

 out of condition rather than to exhaust it. Flax 

 should be indirectly manured. Direct applications of 

 stable manure produce poor results, but when the ma- 

 nure is applied to the preceding crop excellent results 

 are obtained. The best conditions for flax culture re- 

 quire that it should be grown on the same land only 

 once in five years. Dr. Lugger has demonstrated 

 that there are produced, when the roots and straw of 

 flax decay, products which are destructive to succeed- 

 ing flax crops. 76 The food requirements of flax are 

 met when it follows corn which has been well manured, 

 or a sod which has been given the cultivation described 

 for wheat. Flax and spring wheat are much alike in 

 food requirements. 



298. Potatoes. — Potatoes are surface feeders and 

 when grown continually upon the same soil without 

 manure, the yield per acre decreases more rapidly than 

 any other farm crop. Experiments with potatoes by 

 Lawes and Gilbert using different manures gave the 

 following result : 77 



Average Yield per Acre for 12 Years. 



Tons. Cwt. 



No manure 1 19I 



Superphosphate 3 5 



Minerals alone 3 7| 



Nitrate of soda alone 2 4| 



Mixed manures and nitrogen 5 1 7| 



Farm manures, alternate years 4 3| 



