26 



RESULTS OF EXPERIMENTS AT ROTHAMSTED, 



Turning to the yield of nitrogen on the different plots, it is seen 

 that the amounts are almost identical without manure, and with super- 

 phosphate of lime alone, namely, about 33 Ibs. per acre per annum. 

 On plot 8, where a complex mineral manure, including potash six years, 

 but excluding it fourteen years, was employed, the yield of nitrogen is 

 raised to 46*5 Ibs. ; and on plot 7, which received the mixed mineral 

 manure, including potash every year of the twenty, the yield is 5 6 '6 

 Ibs. per acre per annum. Further, without manure, and with super- 

 phosphate of lime alone, there was a decline in the yield of nitrogen in 

 the later, compared with the earlier years. With the mineral manure, 

 including potash in the first six years only, there was a much more 

 marked decline. With the mineral manure, including potash every 

 year, there was, on the other hand, even a slight tendency to an 

 increased yield of nitrogen, in .the later years. 



Thus, then, it is estimated that the plot receiving potash every year, 

 yielded over a period of twenty years, an average of 23-6 Ibs. more 

 nitrogen per acre per annum than the unmanured plot, and this 

 increased yield was associated with an increased growth of Leguminous 

 herbage. Whence comes the 23*6 Ibs. more nitrogen annually taken 

 up per acre on the mineral manured than on the unmanured plot 1 

 The results in Table XII. will afford evidence on this point. 



TABLE XII. 



PERMANENT MEADOW LAND SOILS. 

 Nitrogen, per cent, and per acre, in fine soil, dried at 100 C. 



After 20 years of continuous experiment, samples of soil were 

 taken at three places on each of the experimental plots, and the Table 

 shows the means of determinations of nitrogen in the surface-soils of the 

 unmanured plot, and of the plot receiving the complex mineral manure 

 (including potash), every year. Some control results are also given. 

 Thus, determinations made in samples of the unmanured soil collected 

 in 1870, control those in the samples collected in 1876, after the crops 

 of five more years had been removed ; and, again, the results obtained 

 on samples collected from the mineral manured plot in 1878, control 

 and confirm those obtained on the samples taken in 1876. 



Referring to the main figures, those relating to the samples taken in 

 1876, it is seen, that whilst the percentage of nitrogen in the surface- 

 soil of the unmanured plot was 0-2466, it was in that of the mineral 



