CROPS AND SOIL IMPROVEMENT 



similarly, and that the potato will repay the cost 

 of free use of fertilizer. If the soil is sandy and 

 deficient in potash, the percentage of phosphoric 

 acid may be cut to 8, and the percentage of potash 

 raised to 10, and all these crops will profit thereby. 

 If the nitrogen content in the soil is high, none of 

 these crops may need nitrogen in the fertilizer. 

 This is a general principle, and safe for guidance, 

 though the best profit will demand some modi- 

 fication that readily occurs to the farmer as he 

 studies his crops and their rotation. To illustrate : 

 The corn is given the clover sod or the manure 

 partly because it requires more plant-food than 

 the wheat. It gets the best of the nitrogen, and 

 may need only a rock-and-potash fertilizer, while 

 the wheat that follows may need some available 

 nitrogen to force growth in the fall. There is no 

 fixed formula for any field or crop, and the point 

 to be made here only is that the requirements of 

 many standard crops do not have the dissimilarity 

 usually supposed, except in respect to quantity. 

 A marked exception is found in the oat crop, which 

 does not bear the application of much nitrogen, 

 and often fares well on the remains of the manure 

 that fed the corn, if some phosphoric acid is 

 added. 



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