MANURING FOR POTATOES. 159 



MANURING FOR POTATOES. 

 By Sir J. B. Lawks. 



From New England Homestead. 



Although I consider that the use of complete artificial manures 

 involves too great a cost for their employment in the growth of ordi- 

 nary farm crops, perhaps an exception may be made in regard to 

 potatoes, a crop which requires a large supply both of potash and 

 nitrogen. 



At Rothamstead we have grown nine crops of potatoes in succes- 

 sion upon land which for fifteen years previously had received no 

 yard manure, and the average yield of the last three croi>s has been 

 400 bushels per acre, calculating the bushel to weigh 50 pounds. 

 The manure used each year has been 300 pounds of sulphate of pot- 

 ash, 350 pounds of superphosphate of lime, and 400 pounds of salts 

 of ammonia ; while in another experiment, instead of the salts of 

 ammonia, 540 pounds of nitrate of soda were applied. The produce 

 from both manures has been almost identical. 



The sulphate of potash supplies about one hundred thirty pounds 

 of potash — and we find very nearly the same amount in the crop. 

 The phosphoric acid, on the other hand, is much in excess of the re- 

 quirements of the crop, and it might be reduced one-half. The salts 

 of ammonia and the nitrate each supply about the same amount of 

 nitrogen — eight3'-seven pounds — and of this the crop does not take 

 up more than fifty pounds; there is, apparentl}-, therefore, a con- 

 siderable loss of this substance : but at the same time anv reduction 

 in the amount of these manures would be followed by a reduction 

 in the crop. The loss of this costly manure ingredient is a most 

 serious matter, as unfortunately there is but little prospect of re- 

 covering, in succeeding crops, any appreciable amount of the thirty- 

 seven pounds not taken up by the first. By means of the same 

 mineral manures alone we have grown — over the same period — one- 

 half the crop we obtained by the application of minerals with nitro- 

 gen, the soil having supplied a suflflcient amount of that substance to 

 give a product of two hundred bushels ; but one-half of the minerals 

 applied remained inactive in the soil ; these, however, might be made 

 available to the crop by an application of nitrogen. 



