Experiments in the Culture of Potatoes—Comparisons of Manures—extraordinary Power of Guana, or Sea-fowl Dung, as a Top-dressing—Hints to Proprietors of Islands and Rocks in Scotland.

IN a place which has, for many years, been almost wholly dependent on foreign imports for the common necessaries of life, and where neither commerce nor manufacture finds employment for industry or exertion, there can be no duty more incumbent on persons entrusted with its management, than a due attention to those means that are the most likely to augment its internal resources.

From the earliest period of its establishment (in 1673) to the present time, the most positive orders to favour and encourage agriculture have been sent by the Honourable the Court of Directors. It is, therefore, in obedience to those repeated orders, that I have endeavoured to discover, the capabilities of the soil, and the modes of cultivation the best suited to the circumstances of this island. I have accordingly, in the Abstract of the Laws and Ordinances, and in the papers relating to the goats, embraced every occasion that offered of stating the results, and of introducing, my opinions. I have also, I trust, proved, that immense advantages would arise to the land-holders if they were to allot a certain selected portion of their pasture lands to the culture of corn and artificial grasses, to the planting of trees, and to the introduction of hedge-rows.

Those opinions being founded on a variety of experiments, and the results having been most carefully ascertained, under my own inspection, I can vouch for their accuracy. I feel a confidence, therefore, that whoever may hereafter make similar trials will not be disappointed. But I must here apprise experimenters, that a first crop, from land newly brought into cultivation, is generally much inferior to the succeeding ones.—I found an acre of land, which, upon breaking up, produced only 324 bushels of potatoes, yielded a succeeding crop, planted immediately after, of 522. I ascribe this improvement to the repeated stirring of the soil, by which the fertilizing influence of the rains and atmosphere were admitted. Upon these two crops no manure was used; and as potatoes are known to exhaust fertility, it might have been expected the second crop might have been less instead of greater. Hence, it seems probable, the deterioration of the soil does not take place until some time after the land is brought into cultivation.

Mr. Tull, an Oxfordshire gentleman, who published a Treatise on Husbandry, about forty years ago, speaking of the great advantages of frequently stirring and pulverising the soil, relates, that a little farmer, having prepared his field for sowing, could not raise money to purchase the seed until he had lost the season ; he therefore kept on ploughing, at proper intervals, until the next season arrived, when be compassed to plant his field. At harvest, his crop was so abundant, that its value was more than sufficient to pay the fee simple cost of his field. The effects, from frequent stirring of the soil might readily be determined, by comparing the produce of a square rod of ground, planted with potatoes after being stirred four or five times in as many months, with that of an adjoining space, of the same extent, planted at the time of breaking up.

On my arrival, in 1808, I was desirous of obtaining information upon the modes used here in the culture of potatoes : but I soon perceived, from the vague method of estimating the produce by the returns from the seed sown, without any account being taken of the quantity of land occupied by the crop, that no useful deductions could be drawn, nor any comparison made between the potatoe lands here and those in England.

I learnt, however, that two crops (or more) annually were obtained from the same land; and that these were had, in a continued succession, during a period of 12 or 14 years, without the application of any sort of manure. This, I confess, surprised me. I heard also of "self-sown crops," that is, of leaving in the ground, at the time of digging, a certain portion of the potatoes for a succeeding crop.

This unusual course of husbandry led me to infer that a much better mode might be adopted (which is indeed practised by some of the gentlemen-planters) : and, in order to satisfy myself on this point, I resolved to commence a series of experiments, which should embrace the following essential points in the culture of potatoes; the proper depth of planting—the best sort of seed—the advantage of the row culture—and the improvement by manuring.

The returns of 10 or 15 bushels for one sown, were, in general, deemed good crops; but my experiments have proved that these are very inferior to what can be obtained under a different course of management.

Supposing 13 bushels to be the usual quantity of seed required to plant an acre, the returns above stated would be no more than 180, or 270 bushels per acre. According to the following table it will be seen, that by the new culture, and the aid of manure, the acreable produce of the potatoe lands may be augmented, upon an average, to nearly three times those quantities. What an advantage is this, in a place where the scanty means of labour are generally complained of!

It will be observed, by the table of experiments, that the greatest produce was at the rate of 648 bushels per acre. This was from No. 5, in the division manured with horse dung : but even a greater rate of produce was had from a portion of the unmanured acre, which yielded the 522 bushels before mentioned. I ascertained that 30 feet of the rows of this acre, twice repeated, and taken indiscriminately, produced of fine large potatoes 52 pounds: or, as will be hereafter explained, at the rate of 674 bushels per store.

This was also greatly surpassed by an experiment upon one kidneypotatoe. It was cut in eleven pieces, which were planted in a single row, at one foot asunder, on the 5th of April, 1810, upon ground very highly manured with hog's dung. Nine of the sets only came up, and these occupied one row that measured nine feet. On the 8th of August, 1810 , when the haulm had fallen, the potatoes were taken up, and weighed 21½ pounds averdupois ; which is in the proportion of 929 bushels per acre.

These well ascertained facts will, I hope, draw the attention of the planter to the row culture ; and to establishing farm-yards, and hoggeries, for the purpose of manuring their lands. They might then make experiments for themselves, which I am confident would soon induce them to change their present modes of husbandry; because these are evidently far less profitable, and must, in the course of time, infallibly exhaust, and ruin their plantations.

The spot selected for experiments is in the front garden at Plantation-house. It was exactly a square chain, or the tenth part of an acre ; and was, at first, divided into four equal parts for the manures, according to the black lines in the following diagram :

The figures 12. 9. 6. 3. represent the depths of planting in inches, and the positions of each two rows which traversed the manured and unmanured parts. The numbers 1 to 64 shew the situations of the experiments. The three narrow paths which separated the manured divisions reduced the cultivated space from 16½ to 15 feet: each experiment upon the two rows consisted therefore of 15 feet in length, or of 30 feet of rows ; which, as will be hereafter explained, is the 726th part of an acre.

The manures were evenly spread over the beds in the orders and quantities specified in the diagram ; they were then trenched one spit deep into the soil. The transverse lines mark the spaces for each class of seed, and by crossing the manure divisions they formed 16 squares, containing each four distinct experiments; so that the total number was 64. The soil was rather stiff, being composed of blackish mould intermixed with friable fat clay.

The whole being thus prepared, the seeds were dibbled in at their respective depths, on the 9th of August, 1809, and the produce was taken up on the 30th of November, that is, 113 days after planting.

The following table of the results, exhibits the produce of each experiment, or 30 feet of rows, in pounds ; the weight of the six largest potatoes ; and the computed acreable produce in pounds, and in bushels.

TABLE of the results of the Experiments, exhibiting the number of pounds that each 30 feet of rows yielded, the weight of the six largest Potatoes from each experiment, the computed acreable produce, in pounds and bushels, and the total quantities produced from each sort of seed, at the several depths, throughout the manured and unmanured parts, in the extent of 120 feet of rows.

NOTE.—30 feet of rows are the 726th, and 120 feet the 181.5 of an acre.

The following is an abstract from the preceding table, and is a comparative view of the effects of the several classes of seed, shewing the total produce in pounds.

Class 1. Seed the size of walnuts planted whole, yielded   553½
2. Large seed cut in pieces   588½
3. Eyes of middle sized potatoes   487½
4. Small potatoes planted whole   615½
    Total pounds 2245   

These results will be pleasing to the planters, since they have clearly ascertained that small potatoes planted whole, which would not fetch so good a price in the market as the largest sort, are the best for seed.

The following is a comparative view of the effects of different depths of planting, shewing the total produce in pounds.

1st. Six inches deep, yielded   637   
2d. Three ditto, ditto   549   
3d. Nine ditto, ditto   547¼
4th. Twelve ditto, ditto   511¾
    Total pounds 2245   

By these results, it is proved, that planting at the depth of six inches on stiffish land is the most productive: but if the soil be of a lighter and freer sort, it is probable nine inches, or more, would yield best, because the moisture necessary for vegetation lays deeper in that sort than in a more retentive soil.

The following is a comparative view of the effects of the manures : shewing the total produce in pounds.

1st. The guana ;[1] or, sea-fowl dung at 35 bushels per acre, yielded   639
2d. Horse dung litter at 36 cart loads or 420 bushels per acre, yielded   626
3d. Hog's dung litter, at 35 cart loads, or 420 bushels per acre, yielded   534
4th. No manure   446
    Total pounds 2245

These results decisively prove the great advantage of manuring the lands, which would evidently repay the additional expense, and would maintain the potatoe grounds in good heart. These might, no doubt, be further improved by rotations of corn and green crops, which would prevent those disappointments that arise after perpetual croppings of potatoes for 12 or 14 years without manure. By such a practice, labour becomes useless, its expenses are thrown away; and the lands, originally productive, are, in the end, completely exhausted. This is a fact well known to the planters.

It has already been mentioned that the greatest produce was experiment No. 5 ; which was large seed cut in pieces, planted 12 inches deep, and manured with horse dung litter. Thirty feet of the rows yielded 50 pounds of very fine potatoes, which is at the rate of 648 bushels per acre.

To those who are unaccustomed to such calculations, it may be proper to explain in what manner the results in the Table are computed, from the length of 30 feet of rows.

An English statute acre consists of 10 square chains. This may be more readily comprehended by imagining a space one chain in breadth, and ten in length. As a chain measures 66 feet, it is evident an acre of' the above form will be 66 feet broad, and 660 feet long—and consequently the contents of an acre are 43560 square feet.

If this acre be planted in rows, 2 feet asunder, there may be placed 33 rows in its breadth—and this number of rows, multiplied by 660 feet, will give 21780 feet for the total length of the rows. Then, if this sum be divided by 30 feet, it will be found that this length of rows is exactly the 726th part of an acre—consequently, the produce, in pounds, of anyone of my experiments, multiplied by 726, will give the acreable produce in pounds. To find this produce in bushels, divide by 56 pounds, the weight of a St. Helena bushel.

For example, experiment No. 5, yielded 50 pounds ; multiplying, this by 726, gives 36300 pounds, and dividing by 56, gives 648 bushels, as entered in the Table.

I was, however, accidentally led into this mode of computation because, as I have already stated, the rows had been reduced from 16½ to 15 feet. The readiest way, of determining the acreable produce of a crop of potatoes, or of corn, is first to ascertain the quantity yielded from one rod (that is 16½ feet square), measured upon any part of the field, and then to multiply that quantity by 160 (which is the number of square rods in an acre), the product will be the computed quantity per acre.

January 12th, 1811.

  1. The guana or sea-fowl dung, which is found in considerable quantities upon Egg Island , was first recommended to my notice by the Right Honourable Sir Joseph Banks, President of the Royal Society. "It furnishes," says he, "the loading of an immense number of vessels that are constantly employed in bringing it from small islands, to the main land on the western coast of South America, where it is sold and distributed for the purpose of manure ; which it answers, in a degree, infinitely superior to any other article we have the knowledge of.—A handful is considered as sufficient for several square yards of land, the produce of which is exuberant, in consequence of the force of this application."

    The accuracy of this valuable communication has been most amply confirmed by my experiments in the culture of potatoes, as well as upon grass lands. Thirty-five bushels of the guana, or three cart loads per acre, appear to me, equivalent in effect, to seventy loads of good rot-dung. I should imagine that abundance of this most valuable manure might be had from many of the rocks and islands on the coasts of Scotland.

    The effect of the guana upon grass land is comparatively greater than in the potatoe experiments.—From what cause this proceeds it may be difficult to explain : but as Dr. Priestley found, by experiment, that vegetables throve best when they were made to grow in air made putrid by the decomposition of animal and vegetable substances, it may be inferred that the very strong effluvia which issues from the sea-fowl dung, or guana, together with its being readily washed among the roots of vegetables by the first falls of rain, are circumstances that may possibly render its effects, as a top dressing, greatly superior to those it produces when it is mixed with the soil. By this mixture its powers may be weakened, and a great portion of effluvia, which by some is supposed the proper food of' photo, being retained underground, cannot escape and unite with the atmosphere.

    On the 29th of July, 1808, I marked out a space, on the lawn in front of Plantation-house, which measured one rod in breadth, and twelve rods in length. This was divided into twelve equal parts, or square rods, and numbered progressively from 1 to 12. The guana was reduced to a powder, and sifted ; and upon Number 1 a quart of this powder was evenly strewed by the hand ; this is at the rate of five Winchester bushels per acre ; because 160 square rods, or an acre, would have required that number of' quarts, or exactly five bushels. In the same manner Number 2 had two quarts, Number 3 three quarts, and so on to Number 12, which had twelve quarts, or at the rate of 60 bushels per acre.

    From the 29th of July there were, daily, drizzling rains until the 5th of August, when the effect of this invaluable manure began to appear. On the following day the whole extent of the 12 rods became highly verdant, and exhibited such a contrast to the unmanured part of the lawn, that it had the appearance of having been newly turfed with a finer kind of sod. The effect gradually increased ; and in the first week of October, that is, in little more than two months, the higher numbers, from 6 to 12, (having from 30 to 60 bushels per acre), excited the surprise of every person who saw them, being covered with the most exuberant grass that can be imagined, and having more the resemblance of a crop of young wheat, very thickly sown, than of any grass I ever beheld.

    This is the more remarkable, as at that time, the copious rains which fell in August, and the spring season had made no visible effect on the adjoining part of the lawn.

    It was from a frequent and careful inspection of the above experiments that I have estimated 35 bushels of guana per acre to be equivalent in effect, upon grass lands, to 70 loads of good rot-dung.

    I have been informed that guana is sold at Lima , and at other towns on the coast of Peru , for a dollar a bag, of 50 pounds weight, and that it is much in use there for manuring fruit trees and gardens.

    It is certainly one of the most powerful of manures ; and therefore it is necessary to be cautious in using it. I have observed, when too much is laid upon grass, that it burns and destroys it.—I would therefore recommend, to those who may try it on fruit trees, to begin with not more than three quarters of a pint to each tree, and to trench it, about a foot deep, all round the roots. If the first application be found insufficient, a second, or third, may be given at intervals of two or three months ; or, a better mode, perhaps, of determining the quantity of guana proper for each fruit tree, would be to select about a dozen trees of the same kind and size, and to vary the quantities, by an easy progression, from three quarters of a pint, to one or two quarts, or more, to each tree.
    A. B.

 Section III