FIELD CROPS. 141 



*'show in a striking manner the unreliability of the specific gravity 

 method of determining starch in potatoes." 



A summary is given of considerable literature on fertilizing pota- 

 toes. On the basis of the chemical aualj'sis of potatoes, the fertiliz- 

 ing constituents removed by a crop of 200 bu. per acre is calculated 

 to be 37 lbs. of nitrogen, 16 lbs. of phosphoric acid, and 58 lbs. of 

 potash. Twentj^-six brands of so-called potato fertilizers were exam- 

 ined, and only 8 were found to resemble the above in proportion of 

 constituents, and these contained much more phosphoric acid. 



Fertilizer experiments with potatoes, B. Sjollema {Jour. 

 JjCOidw., J^7 {1S99), JVo. '2.^ 2U*- lOo-lJfO). — This is a report on a series 

 of fertilizer experiments which have extended over a period of 17 

 years. In a comparison of barnyard manure and chemical fertilizers, 

 the 3'ield was about the same on each, but the starch content of the 

 tubers was noticeabl}^ lower in the former case, being onh' 11,25 per 

 cent as against 16.15 per cent in the latter. Barn3"ard manure was 

 plainlj" unfavorable to the fullest development of starch. This con- 

 clusion, based on experiments in which the barnyard manure and chem- 

 ical fertilizers were applied to different plats, was confirmed by other 

 experiments in which each was applied to the same plat in different 

 seasons. 



In a comparison of sulphate of ammonia and nitrate of soda as 

 sources of nitrogen for potatoes, the yield of tubers with the former was 

 7.3 per cent less than with the latter. At the same time their starch 

 content was less by 0.5 per cent. As a result, the amount of starch 

 produced was 11 per cent less on sulphate of ammonia than on nitrate 

 of soda. This result may probably be explained, the author suggests, 

 bv the fact that nitrate of soda is a more readily availal)le plant food. 



In a stud}' of the influence of different kinds of manures on starch 

 content, a complete chemical fertilizei- was compared with other ferti- 

 lizers identical except that either nitrogen or phosphoric acid was 

 omitted. The complete fertilizer applied in the usual quantities pro- 

 duced 31,500 kg. of tubers with a starch content of 16.15 per cent. 

 The fertilizer containing no phosphoric acid produced 28,500 kg. of 

 tubers with a starch content of 15.05 per cent ; and the fertilizer con- 

 taining no nitrogen produced 27,800 kg. with a starch content of 16.15 

 per cent. It appears that either phosphoric acid favors the formation 

 of starch, or that nitrogen is unfavorable to it. It was shown by other 

 experiments that both inferences are correct; but when the application 

 of fertilizer was doubled in each case, the complete chemical fertilizer 

 produced a starch content of 19 per cent, the fertilizer containing no 

 phosphoric acid 18.1 per cent, and that containing no nitrogen 18.6 

 per cent — that is, nitrate of soda does not materially hinder the for- 

 mation of starch provided all other elements of plant food are present 

 in sufficient quantities. 



