402 INVESTIGATION BY CULTURE EXPERIMENTS 



Where organic nitrogen was applied in rape cake, the additional 

 8 pounds of soluble nitrogen produced only two thirds of a ton in- 

 crease, which would be worth less than the cost of the nitrogen, at 

 the price used. 



It may be stated that the first crop of mangel-wurzel (1876) on 

 plot O8 was 5.45 tons, while the same plot produced 6.95 tons in 

 1898 and 7.75 tons in 1900. Plot N4 produced 25.05 tons in 1876, 

 and several plots produced still higher yields, the highest being 

 31.45 tons on plot ACi. 



Since 1904, the 200 pounds of sodium chlorid has been omitted 

 from one half of plot N4, which receives sodium in the nitrate. 

 The subsequent yields for this half have been 24.69, 16.69, an ^ 35- Z 5 

 tons per acre for the years 1905-1907, or distinctly more than where 

 the common salt was included, as will be seen from Table 716. 



Of special interest is the evident effect of the potassium applied 

 to plots 2 for 1895 and since. The previous records indicate that 

 the heavy applications of manure had furnished sufficient phos- 

 phorus for the crops grown, and the yields since 1895 plainly show 

 that potassium was the limiting element wherever nitrogen had 

 been applied in addition to the farm manure. Since phosphorus 

 is also applied to plots 2, it is impossible to determine what in- 

 crease would have been made by potassium without the added 

 phosphorus; but on plots A2, AC2, and C2 the yields since 1895 

 have averaged about 5 tons more than on the No. i plots. The 

 sodium applied in the. sodium nitrate on plot Ni appears to produce 

 almost the same effect as the potassium applied (since 1895) to 

 plot A2. It will be observed that phosphorus produced an appre- 

 ciable effect on N2 from 1876 to 1890. 



As an average, one ton (2000 pounds) of mangel-wurzel contains 

 about 3.6 pounds of nitrogen, .5 pound of phosphorus, and 6.6 

 pounds of potassium, and the average requirements for such an 

 enormous crop as grew on plot AC2 in 1907 would be about 175 

 pounds of nitrogen, 24 pounds of phosphorus, and 330 pounds of 

 potassium, for the roots only. If we assume the farm manure to 

 have 10 pounds of nitrogen, 2 pounds of phosphorus, and 8 pounds 

 of potassium per ton of 2000 pounds, the annual applications now 

 being made to plot AC2 contain about 340 pounds of nitrogen, 

 60 pounds of phosphorus, and 360 pounds of potassium. On this 



