Reference has been so repeatedly made in the preceding pages to the Rothamsted experiments on manures, that it may form a fitting conclusion to the present treatise to give a short account of these famous experiments.

In describing these experiments, the author has remarked elsewhere[256] "that, in respect of their wide scope, dealing as they have done with almost every department of farming, the elaborate care and accuracy with which they have been carried out, the length of time they have been in progress, and, lastly, in respect of the important bearing their results have had on agricultural practice, these famous experiments may be justly described as unrivalled by any other similar ones."

Started on a small scale in 1837 by Sir John (then Mr) Lawes, they were placed on a systematic basis in 1843, in which year Sir John Lawes associated with himself Sir (then Dr) J. Henry Gilbert. They have thus been in progress for a period of fifty years—a fact which was celebrated a few months ago by the presentation of numerous congratulatory addresses from various learned and agricultural societies to the distinguished investigators, and the erection of a memorial granite slab at Rothamsted. What increases the feeling of gratitude due to Sir John Lawes by the agricultural community, is the fact that the entire expense of conducting these experiments has been borne by himself, and he has further most generously handed over to the nation a large sum of money and a certain area of land for carrying them on in perpetuity.

Nature of Experiments on Crops and Manures.

The earliest systematic experiments were on turnips, and since then almost every common crop has been experimented on. Table I. (p. 562) is a list of the different experiments, with their duration, area, and number of plots.

Soil of Rothamsted.

Before describing the more striking results of these experiments, it may be advisable to say that the elevation of the land at Rothamsted is about 400 feet above sea-level; that the average rainfall is about 28 inches per annum; and that the surface-soil is a heavy loam, and the subsoil a stiff clay, resting on chalk.

TABLE I.—List of Rothamsted Field Experiments.

Wheat Experiments.

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).

Table III.—(b.) Results of subsequent Forty Years (1852 to 1891).

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.

The next experiments we shall describe are those on the influence of farmyard manure on the wheat crop when grown continuously.

TABLE IV.—Wheat grown continuously with Farmyard Manure (14 tons per annum).

It will be seen from the above results, which contain merely a selection from a very much greater number of experiments, that farmyard manure gives as good an average over the forty years as most of the artificial mixtures do. That this is due to the nitrogen it contains, is strikingly illustrated by the fact that mixed mineral manures alone give less than half the return, and also by the fact that ammonia salts alone give a return twice as great as mineral mixtures; while, lastly, the mixture of mineral manures and ammonia salts gives but a slight increase over that obtained with ammonia salts alone.

The remaining results, selected from a much larger number, need no comment, and we shall give them in tabular form.

Table V.—Wheat grown continuously with Artificial Manures, Farmyard Manure, and Unmanured.

Average of Forty Years (1852-91).

TABLE V.—continued

TABLE V.—continued

TABLE VI.—Experiments on the Growth of Barley for Forty Years, 1852-91.

TABLE VI.—continued

TABLE VI.—continued

TABLE VII.

Experiments on the Growth of Oats, 1869-78.

TABLE VIII.—Experiments on Root Crops: Swedish Turnips.

Fifteen Seasons, 1856-70.¹ Roots and Leaves carted off the Land.

TABLE VIII.—continued

TABLE VIII.—continued

TABLE IX.—Experiments on Mangel-Wurzel.

Average of Sixteen Seasons, 1876-92. Manures per Acre per Annum.

TABLE IX.—continued

TABLE IX.—continued

TABLE X.—Experiments with different Manures on Permanent Meadow-land.

Thirty-six Years, 1856-91.

TABLE XI.—Experiments on the Growth of Potatoes.

Average of Five Seasons, 1876-80.¹

TABLE XII.—Experiments on the Growth of Potatoes—Continued.

Average of Twelve Seasons, 1881-92.

FOOTNOTES: