Yields of Earlier and Later Years Compared. 29 



the soil and season, the produce was somewhat higher in the 

 later years ; where the resources of the soil were overtaxed 

 by the use of a large amount of ammonia salts every year 

 (plot 10a), the produce diminished ; but where an excess of 

 every constituent was annually applied (plot 2) the crop 

 enormously increased as the experiment proceeded. These 

 generalisations are based upon the first three lines of figures 

 in the foregoing table. 



Taking the final twelve years, the table further shows that 

 the average annual yield was, without manure (plot 3) much 

 the same over the whole period ; that, notwithstanding the 

 exhausting effects of applying ammonia-salts every year 

 (plot Wa), the annual diminution of produce under their 

 influence was proportionally less during the latter half of 

 the last twelve, than of the whole nineteen years of their 

 use ; that, where ammonia-salts and all mineral constituents, 

 except silica, were liberally supplied every year (plot 7), the 

 produce of grain increased and that of straw somewhat 

 diminished ; lastly, that where an excess of every constituent 

 required by the crop was annually applied, as in the farm- 

 yard manure (plot 2), the rate of increase from year to year 

 was not so great during the later as during some of the 

 earlier years. 



Upon the whole, it must be concluded that the later years 

 were, on the average, slightly more favourable to the crop 

 than the earlier ones. The fact of the unmanured plot 

 maintaining its produce throughout the whole twenty years 

 is, then, probably in some degree due to the better average 

 of the seasons themselves in the later years. Had it been 

 otherwise, the unmanured produce would have shown some 

 slight decline in the later years, or rather, some slight- 

 excess in the earlier ones, due to the accumulation of many 

 previous courses of manuring 1 and cropping. In the report 

 of the second twenty years' experiments, and with the results 

 of forty years' continuous growth before them, the investi- 

 gators do not introduce a comparison between the first 



