Ill 



I: I 



32 



were moist. Next, the stones are removed ; first those retained by a 

 sieve of 1-inch mesh, next by a sieve of one. half-inch mesh, and then 

 by a one-foarth-inch sieve. All that passes the ono-fourth-inch sieve 

 is termed the mould. Portions of this are very finely powdered and 

 sifted for analysis ; and the weights being recorded at each stage of 

 preparation, and the water lost on drying at 100° C. being determined 

 on the finely-powdered mould, all results of analysis are calculated 

 into percentage on the so-determined dry mould. From the same data 

 the amount of dry mould per acre is calculated, and upon this the 

 amount of nitrogen per acre. It will be seen further on, that not- 

 withstanding the means adopted to secure uniformity, the amounts of 

 dry mould per acre calculated for a given depth, from the samples 

 taken, vary considerably for the same field at diffc'rent times, accord- 

 ing to the dryness or wetness of the season, the condition of the land 

 as affected by the crop, the mechanical operations, and other circum- 

 stances. The amounts also vary very considerably for the soils of 

 adjoining fields. 



Nitrogen in the Soils of the Experimental Wheat Plots. 



The first series of determinations of nitrogen to which attention 

 will be called relates to those made in the soils of some of the plots of 

 Broadbalk field, which has now grown wheat for thirty-nine years in 

 succession, and the yield of nitrogen in which, on the plots receiving 

 no nitrogen in manure, has been given in Table I. It will be remem- 

 bered that, under those conditions, there was a very marked decline 

 in the annual yield of nitrogen in the crop, both without any manure, 

 and with a mixed mineral manure used alone. 



The first wheat crop of the series was harvested in 1844, and 

 although isolated samples of the soil were taken in the early years, it 

 was not until 1856 that any were collected on the plan now followed. 

 At that date only four plots were sampled, and only to the depth of 

 the first 9 inches. Eight samples were, however, taken from each 

 plot, each 12 by 12 inches area, and the eight were mixed together. 

 In 1865, samples were taken from eleven plots, from eight places on 

 each plot, each sample 12 by 12 inches area, and this time to a depth 

 three times 9 inches, or to a total depth of 27 inches. Lastly, in 1881, 

 twenty plots were sampled ; six samples, each 6 by 6 inches area, 

 were taken from each plot, and in each case to three depths of 9 inches 

 each, or in all to 27 inches. 



Thus, it is only in 1865 and 1881 that we have any considerable 

 series of samples, and the nitrogen determined in them ; that is, in 

 1865 after the twenty-second, and in 1881 after the thirty-eighth 



M/' 



