Recurring again to the quantity of manure necessary to grow thirty-six bushels of wheat, I would ask, why limit yourself to so small a crop? The difference in the cost of your manuring a field, and my manuring it, is more than made up by the increase of fourteen bushels of wheat and the corresponding increase of straw, even if the land did not improve every year by the application; and as the seed, rent, labour, and liabilities of the land are the same whether you grow a small crop or a large one, why not have it as large as possible? Again, if I applied far more manure than was necessary, I ought to have had the crop equally good throughout the field; but on the ridge of the hill, where the soil was thin and poor, neither straw nor wheat were so good as they were where it was deeper and richer. My own opinion is, that the plant is never able to extract from the soil all the manure, and therefore it ought to be brought up to a good standard before good crops can be expected. I am not satisfied with any analogy that I can think of, but the best that occurs to me is that of a cloth in a dye- copper. You can never get it to absorb either all or half the colouring matter, and if you don't use far more than is taken up by the cloth, you will never obtain the desired results. Besides, in chemical combinations it is desirable to use far more than the chemical equivalents, or the experiments don't succeed. I perceive that you intend to use guano next year, and that you intend to use it along with the seed. I trust it will not be sowed in contact with either the seed or the quicklime, which you proposed to use in some of your land. The best time I have found for applying guano is in wet weather, just when vegetation is making a start in the spring—say the last week in March, or the first week in April—as I fear a large part of the soluble portion of it would be washed away by the rains of winter. It is true we have had none this winter, but when shall we have such another? Did you ever use woollen rags as manure? They ought to be excellent, as they are almost all albumen, and are, I fancy, to be had at a very moderate price, not far from you. Can you inform me what it is that causes the land to be clover-sick? If it is the abstraction of something from the soil, what is that something? Sir Humphrey Davy said that a dressing of gypsum would prevent it; but clover does not succeed here (even when dressed with gypsum), if sowed every four years. One reason why I think so small a quantity of manure will not succeed, is based on the theory of excrementitious secretion. Decandolle proved that this secretion took place, but he did not succeed in proving that it poisoned the land for a similar crop. I can only reason from analogy, and it does not follow that an analogy drawn from animal life will hold good when applied to plants; but if we were to feed an animal with pure gluten and pure starch, with the proper quantity of phosphates, &c., are we to suppose it would have no excrements? Let this be applied to plants: are we to suppose that the plant assimilates all that is absorbed by its roots and leaves? When that which is absorbed is what would enter into the composition of the plant, is it not more rational to suppose that the inorganic and gaseous constituents only combine in fixed proportions, and that although the plant may absorb a much larger proportion of one than is required, the surplus is discharged excrementitiously, and perhaps may be unfitted for entering into the plant until it has undergone a decomposition? In conclusion, I trust you will pardon my frankness in so boldly canvassing your opinions; but it is in this collision of opinion that the truth will be elicited, and if I judge you aright, it is that you wish to discover whether it harmonizes with your preconceived notions or not.
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LOW MOOR, 1st May, 1845.
HENRY BRIGGS, ESQ.
I duly received your pamphlet on the use of lime, for which I am much obliged, and am delighted to perceive that you confirm the idea (expressed in my pamphlet on the growth of wheat every year on the same land) that the excessive use of lime is ultimately injurious to the fertility of the soil to which it is applied. This, coming from a gentleman of your reputation and experience, will, I hope, induce someone capable of performing the experiment to endeavour to ascertain with precision how much lime it is desirable to apply to an acre to give the best results, and with the least waste, assuming that the land contained little or none previous to the experiment; and it would also be desirable to ascertain whether it is better, in an economical point of view, to apply a small quantity every year, or a larger quantity every third or fourth. My own opinion is in favour of the former method, except that it is difficult to get it ploughed in, particularly in wet weather, immediately after spreading (which is essential where you grow wheat on the same land every year) without injuring the feet of the horses. You speak of ten days or a fortnight being necessary to neutralize caustic lime, but our horses had their feet injured by it six weeks after it had been spread on the land, last year, although the weather had been wet almost the whole of the time, say from the beginning of February to the middle of March. You appear to think that lime will replace silica in the wheat plant. Whose authority have you for this? It will be very important to establish this supposition, but I fear it is too good news to be true. On referring to your letter, I find you don't say what I supposed you did, but that the lime liberates the soluble silicates, potash, &c. This may be, and certainly the beneficial effects of lime in growing wheat are not to be explained by any other hypothesis with which I am acquainted. I am this year trying some experiments to ascertain (if I can) the cause of clover- sickness, and I hope to be in a position to say whether your supposition that lime, gypsum, &c. will prevent it, is correct. My experiments so far are opposed to this theory, but it is not very safe or philosophical to draw conclusions from one or two experiments only. I doubt the possibility of making silicate of soda by merely mixing lime, sand, and salt together, as my chemical friends tell me this cannot be accomplished unless the silex and the alkali are fused together. If a soluble silicate of soda can be made in the way you mention, it will be a great saving of expense. Has it been tried? You have no doubt seen a report of the enormous crop of wheat grown in a field in Norfolk last year (90 bushels to the acre), and that the Royal Agricultural Society have determined to have the soil analyzed by Dr. Playfair. This is very desirable, but as Dr. Playfair is more of a lecturing than an analyzing chemist, I think it is very necessary that his analysis should be checked by another, made by the most eminent chemist that Europe can produce, for 90 bushels is so unheard-of a crop, that no expense should be spared which would enable us to ascertain what the soil contained to enable it to produce such a crop, which is the more remarkable as the field seems to have been a good many years under the plough. As your Wakefield Farmers' Club has many wealthy members in it, allow me to hint the desirableness of your undertaking this analysis, which, if properly performed, will be worth a thousand times more than its cost. When you are aware that even Davy missed 16 per cent. of alumina in one of his analyses and that the chemists of the present day don't seem to have detected the potash which exists so abundantly in potato-tops, you will, I think, agree how exceedingly important it is that such analysis should be checked by others, made without any communication between the parties. You speak of an original letter of Liebig's appearing in the "Farmer's Journal." On what subject is it? as I have no means of referring to the periodical in question. Does it throw any light upon the new manure for which he is said to be taking out a patent? You speak of humus and humic acid. What do you understand by humus? as, according to Liebig, humus sometimes means one thing and sometimes another, and he appears to treat it very much as modern chemists treat phlogiston, as something which they don't comprehend, but which they need to explain the phenomena of vegetation. If you are a believer in humus, what is it composed of, and how does it act in forwarding vegetation? I suppose you will reply, By combining with oxygen and forming humic acid. But would not the theory of the decomposition of carbon do quite as well? I don't perceive the injurious effects of quicklime upon grass land which you anticipate in your paper, but the contrary, and the more caustic it is the more beneficial is its action, so far as I can judge from my own experiments; and it is my practice in liming grass land to spread it as soon as I can get it into the state of flour. I shall be glad to hear the result of your electrical experiment—at present I am rather sceptical on the subject.
P.S.—Am I to suppose that you have abandoned the idea of manuring an acre of wheat for thirteen shillings?
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THE CULTIVATION OF WHEAT.
October 1st, 1852.
To the Editor of the "Manchester Guardian."