Yield of Wheat per Acre per Annum. 77 



gives somewhat too high a result for the country at large in 

 seasons of great abundance, and too low a result in un- 

 favourable seasons. Accordingly, in some seasons, instead of 

 the actual average indicated by the experimental plots, a 

 higher or a lower figure has been adopted ; and especially in 

 the case of some of the then (1880) recent bad seasons a 

 higher one was taken. 



Independently of any such admitted differences between 

 the so directly calculated and the actually adopted estimates 

 for individual years, the question arises Whether the 

 average result indicated by the several selected plots remains 

 as applicable as heretofore ; or whether the produce of some 

 is annually declining, or that of others annually increasing, 

 irrespectively of the influence of season, so as to vitiate the 

 continued applicability of such results for the purposes of 

 such an estimate ? This point has already been discussed in 

 connection with the forty years' experiments on the con- 

 tinuous growth of wheat, so that it is only necessary here to 

 repeat that the produce of the unmanured plot is gradually 

 declining from exhaustion, that the farmyard manure plot is 

 increasing in fertility, and that there is no evidence of 

 material increase or material decrease on either of the plots 

 receiving ammonia-salts other than that due to season. 

 Comparing the direct average of the experimental plots with 

 that actually adopted as the average for the United Kingdom 

 each year, the experimental plots indicate for the whole 

 twenty-eight years (i.e., up to 1879-80) about three-quarters 

 of a bushel less per acre per annum than the actually 

 adopted estimates founded upon them. 



Taking the average of the twenty-eight years' adopted 

 estimate of produce per acre as 100, the first column of 

 Table XVII. shows the deviation from this general average 

 for the whole period, over the first eight, the second eight, 

 the third eight, and the last four years of the twenty-eight ; 

 and the second column shows the deviation, from the same 

 standard, of the average produce per acre on the selected plots. 



