282 Fertilizers 



from combinations not readily accessible to other plants. 

 In fact, they respond so promptly to applications of this 

 element that frequently too little attention is given to 

 the supplies of the other elements ; yet in order to obtain 

 satisfactory yields, these must also be added. An anal- 

 ysis of the turnip, for example, shows it to be rich in 

 potash; hence it must naturally be a voracious feeder 

 upon compounds containing this element, and while it 

 seems to obtain it more readily from soil sources than 

 many other plants, these supplies should not be depended 

 upon, even on good soils, to meet its entire needs in this 

 respect. A liberal supply of nitrogen is also demanded, 

 particularly during the early growth. An application of a 

 fertilizer containing 20 pounds of nitrogen, derived in part 

 from nitrate, 40 of phosphoric acid, derived in large part 

 from phosphates, and 40 of potash, derived from muriates, 

 would be a fair dressing on soils of good character. On 

 the poorer soils, the application of the constituents of the 

 same kind and forms should be very largely increased. 



In these crops, as in those already mentioned, it is es- 

 sential and success depends upon this as much as upon 

 any other factor that the growth should be continuous ; 

 and in order that there shall be no delay in this respect, 

 there must be an abundance of available food always at 

 their command. 



TUBER CROPS 



In many sections the potato and sweet potato are 

 grown for roughage. For these crops no different fer- 

 tilization is recommended than that already outlined 

 (Chapter XIII) for the crops when grown for market, 

 though in the case of sweet potatoes, soils not adapted 

 for the growth of marketable tubers may be used. 



