The first experiments we shall refer to are those on wheat, since they are among the oldest, and their results the most striking of any.
Unmanured Plots.
Wheat has been continuously grown year after year on three plots for fifty years, without the application of any manure whatever.
We shall first give the results of the first eight years as illustrating the effect of season, which accounts for the irregular results obtained. But for the difference in seasons, we should expect to find a steady decrease in the amount of produce; and this is shown in taking the average of groups of years, as we shall do in the next table.
Wheat grown continuously on same Land (unmanured).
Table II.—(a.) Remits of first Eight Years (1844 to 1851).
| Year. | Bushels. |
| 1844 | 15 |
| 1845 | 23-1/4 |
| 1846 | 18 |
| 1847 | 16-7/8 |
| 1848 | 14-3/4 |
| 1849 | 19-1/4 |
| 1850 | 15-7/8 |
| 1851 | 15-7/8 |
| Average of 8 years | 17-3/8 |
Table III.—(b.) Results of subsequent Forty Years (1852 to 1891).
| Grain | Weight per | Straw | |
| (bushels). | bushel. | (cwts.) | |
| 20 years (1852-1871) | 14-1/2 | 57-5/8 | 13 |
| 20 years (1872-1891) | 11-1/2 | 58-3/4 | 8-5/8 |
| 40 years (1852-1891) | 13 | 58-1/4 | 10-5/8 |
| 49th season (1891) | 9-3/8 | 59-1/2 | 7-1/2 |
It is interesting to notice the comparatively slight decrease which has taken place in the yield of wheat during these fifty years. With such wide variations, due to season, it is extremely difficult, as Sir J. Henry Gilbert has pointed out, to estimate rate of decline due to exhaustion. Excluding the very bad seasons, this may be reckoned at from one-fourth to one-third of a bushel per acre per annum. The return of the first year is 15 bushels, while the yield of the forty-ninth season is 9-3/8 bushels. The average of the returns obtained during these fifty years is really in excess of the average yield of the principal wheat-producing countries in the world. This is truly a most astounding result.