1. To show the natural produce of the land, one part was to have no manure whatever.
2. Was to have twelve tons per acre of farm-yard dung.
3. Was to have six tons of dung, and one cwt. each of guano and dissolved coprolites; and
4. Was to have two cwt. of guano and two cwt. of the coprolites.
Other substances might be tried as additions, but these were to be the standard experiments.
Mr. Cholmeley's turnips, grown on a loamy soil had the heaviest crop on No. 3, the dung, coprolite, and guano, beating the farm-yard manure by some 5-3/4 tons per acre.
Mr. Johnson's experiments were tried with various manures singly; and his Peruvian guano gave the greatest weight of the class of substances tried; but 10 cubic yards of farm-yard manure had previously been applied to the whole land.
Mr. Maulevere's heaviest weight, also applied singly, was with the 12 tons of dung; but only 14 cwt. more than the dressing with 2 cwt. of coprolites. This soil was a light clay.
Mr. Newham's on a limestone soil, were the heaviest with No. 3--the same as Mr. Cholmeley's--and were 16 cwt. heavier than an application of dung alone.
Mr. Outhwaite's, on a hungry gravel, were the heaviest, with 9-3/4 tons of dung and 2 cwt. of guano, for all the land had been dunged at this rate, and exceeded 14-1/2 tons of dung by 2 tons 9 cwt. per acre.
Mr. Scott's were the heaviest on No. 4,--the guano and coprolites, and 1 ton 7 cwt. more than 20 tons of dung,--his soil was a strong loam.
Mr. Wailes's were the heaviest, with 4 cwt. of coprolites, showing an increase over 20 tons of dung of 2 tons 9 cwt. per acre; the soil is a useful loam.
The first fact which strikes the observer, is, that as a general rule, there is not only an addition to the crop by the addition of those artificial manures, but there is, in some cases, more absolute crop produced by them than by farm-yard manure alone.
Now to bring this to the test of figures, the coprolites at £5 per ton, and the guano at £10 per ton, will be at the rate of 2 cwt of each, £1 10s per acre. Now assuming this to be equal to 20 tons of dung per acre, we should require to be able to produce the dung at 1s 6d per ton to cost us the same money. But it can be neither produced nor purchased at any such money. In the whole of the cases referred to, the manure is most costly, and yet we find hardly any case where there is not an addition to the crop, of say two to three tons of turnips per acre, by such an increase of manure as the guano. Now, if a ton of turnips be worth 10s., or even 9s, there is at once an element of repayment; for, if a soil be in a condition to give a large crop of turnips, it is almost certain to be capable of giving a large crop of any other plant to succeed.