WHEAT. 160 



nips (fed on the land), barley, peas, wheat, and oats, before 

 the commencement of the experiments in 1843-44. The plot 

 then grew eight crops of wheat without manure, to 1850-51, 

 before the commencement of the period of 40 years to which 

 the averages which have been quoted refer. Although at 

 the conclusion of the five-course rotation since manuring 

 above described, the land would doubtless be, in an agri- 

 cultural sense, so far exhausted as to require re-manuring, 

 there can be no doubt that there would nevertheless be 

 some accumulation due to comparatively recent manuring 

 and cropping. It would be supposed, however, that the 

 growth of wheat for 8 years in succession without manure 

 would remove most, if not all, accumulation which could be 

 attributed to comparatively recent treatment. Indeed there 

 can be little doubt that the land would suffer more or less 

 exhaustion during these 8 years ; but, as serving to counteract 

 the tendency to decline in yield from exhaustion during that 

 period, it happened that, taken together, those eight seasons 

 were of more than average productiveness. 



The question of the rate of decline due to exhaustion, as Fall in 

 distinguished from fluctuation due to season, has been made -P ro ^ Mce 

 the subject of elaborate calculation and discussion, which haustion. 

 cannot be gone into here; but the general result may be 

 stated as follows : — 



Assuming, for reasons which were fully considered, the 

 standard produce of the unmanured plot to have been 16 

 bushels per acre independently of material exhaustion, there 

 was an average decline from year to year of little more than 

 one-sixth of a bushel over the 40 years 1852-91. It remains 

 to be seen what will be the result in the future ; and whether 

 a point has already been, or will in time be reached, at which 

 the produce will remain constant, excepting so far as it is 

 influenced by the fluctuations of the seasons. 



It is estimated that over the period of 30 years, 1851-52 Yield of 

 to 1880-81, the unmanured plot yielded an average of 18.6 ^J 09 ^ 

 lb. of nitrogen per acre per annum in the crop, and lost a loss of 

 minimum of 10.3 lb. in drainage, in all 28.9 lb. ; whilst, on f^-^ n e in 

 the mixed mineral manure plot (5), it is estimated that the 

 crop removed an average of 20.3 lb. of nitrogen, and that 

 at least 12 lb. were lost by drainage, or in total 32.3 lb. 

 Further, it is estimated that the soils lost to the depth of 

 27 inches about two-thirds of these amounts ; leaving, say, 

 10 lb., more or less, to be otherwise accounted for. Of this, 

 the rain, &c, would supply 5 lb., or perhaps rather more, 

 and the seed about 2 lb., so that there is but little to be 

 provided from all other sources. Further, as at the com- 

 mencement the soil was, agriculturally speaking, exhausted, 



VOL. VII. L 2 



