THE ROTHAMSTED EXPERIMENTS 401 



favorable conditions, no nitrogen salts were applied for those years. 

 For the same reason the records for plots N$ to N8 and A3 to A8 

 are not used for 1903. The Rothamsted Station reports that, 

 owing to very heavy rains in November, 1894, flooding the lower 

 parts of the experimental mangel field, and washing soil from the 

 farm-manure plots, especially on to plot 03, and to a less degree 

 on to plot N3, there is no doubt that the results from those plots 

 are too high for 1895 and each year since. Of late years no data are 

 reported from plot 3, but the No. 8 plots are sufficient. 



As explained in the table, 500 pounds of potassium sulfate has 

 been applied since 1895, in addition to the other regular treatments, 

 to plots Oa, N2, A2, AC2, and 2; and for 1903 and since the 

 application of potassium and the extra nitrogen (8 pounds per acre) 

 has been discontinued on plots Oy, Ny, Ay, ACy, and Cy, but in- 

 stead those plots have received the full minerals, except potassium. 



The " minerals " regularly include 392 pounds of acid phosphate, 

 500 pounds of potassium sulfate, 200 pounds of magnesium sul- 

 fate, and 200 pounds of common salt (sodium chlorid) ; but from 

 1896 to 1902 the acid phosphate was replaced throughout by slag 

 phosphate. 



The mangel leaves are each year spread over the respective 

 plot, and thus returned to the soil. 



It had been suggested that plants with large leaf surface, like 

 the mangel, could probably secure sufficient nitrogen from the air, 

 in the form of ammonia or possibly as free nitrogen, for their full 

 requirement, provided a small amount of available nitrogen was 

 furnished to give the plants a good start; and because of this the 

 special 8 pounds of nitrogen were applied to plots Oy, Ny, Ay, and 

 Cy until 1902, after which the treatment for those plots was 

 changed as stated. 



Where no other nitrogen was supplied (plot Oy), the 8 pounds 

 increased the yield of mangel-wurzel by 1.36 tons as an average of 

 25 years. At $1.50 per long ton this increase would be worth $2.04 

 per acre, while the nitrogen would cost only $1.20 at 15 cents a 

 pound. Two points must be kept in mind, however; first, that the 

 total crop on plot O8 was produced at a loss; second, that the 

 increase from the phosphorus and potassium applied to plot O6 

 was worth less than 10 per cent of the cost of those elements. 



