Henry Briggs, Esq
I duly received your obliging letter in reply to my pamphlet on the growth of wheat year after year on the same land, and now offer my rejoinder to your remarks. You seem to consider the expense is too great under the system pursued by me; and that it was more than was required by the crop, is proved in my opinion by the fact that the fertility of the land is very much augmented since the commencement of the experiment in 1841: as my first crop with guano alone produced only 27 bushels per acre, whilst this year from guano alone the produce was 42 bushels. But still I think that your allowance of manure is far too little, and not exactly what I should apply, and I shall frankly state my objections and opinions, in the hope that they may elicit a reply from you, as it will be from discussion and the experiments instituted to test the various theories propounded, that agriculture will be most materially benefited. You state that Liebig’s present theory is, that plants obtain the necessary oxygen, hydrogen, carbon, and nitrogen from the rain and atmosphere, and that the plants merely require the supply of inorganic constituents, and that you are inclined to agree with him. My copy of his work on the Chemistry of Agriculture is his first edition; and I don’t know how far he has since modified or altered the opinions therein expressed, which are in some degree at variance with each other. He states that it may be received as an axiom in agricultural chemistry that the nitrogen of the atmosphere is never assimilated by plants, except in the form of ammonia or nitric acid. He certainly states that plants and animals derive their nitrogen from the atmosphere; but why, if this be true, does he attach so much importance to the excrements (particularly urine), of men and animals being husbanded with so much care? and he states that for every pound of urine wasted, a pound of wheat is thrown away. But even if he said it was utterly worthless, every practical farmer who has tried it knows how exceedingly valuable it is. It may be said there are other ingredients in urine besides ammonia, and these are what make it valuable; and in reply to this I would ask what is it that makes the ammoniacal liquor from gasworks so valuable? There are no phosphates or alkalies there, and yet what a powerful stimulant it is. Again, Liebig states that the carbon is derived from the atmosphere; but to say nothing of the argument which might be deduced from the advantage which is derived by plants from having their soil loosened about their roots, the experiments of Dumas and Boussingault prove that a tree which was cut off below the branches expired a large quantity of carbonic acid. It may be asked how I know this was not precipitated by the rain. I don’t know; but if the plant would assimilate this, why should it not assimilate that which arises from the decomposition of the carbonaceous matter in the soil? My idea is that it does both, and that carbon in the soil does good if it offers an abundant supply of carbonic acid to the plant when it is in a condition to appropriate it. Your allowance of lime appears to me to be far too small, for if any reliance can be placed on my experiments, lime can be profitably used to far greater extent than you seem to imagine. And, again, you seem to think that where there is plenty of silex in the soil, the plant will be able to obtain as much as it requires. I think that it is quite necessary that the silex should be in a soluble state, as I think that it is not only desirable that all the elements necessary to fertility should be in the soil, but that they should be in such a form that they can be assimilated by the plant. Some of our compounds for producing fertility may perhaps be as absurd as it would be to give muriatic acid to a man troubled with indigestion, because free muriatic acid is found in the stomach of a healthy person. Let me recommend you to try both silex and magnesia in a soluble state, and I think you will be satisfied with the benefit derived from their use.
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.
LOW MOOR, 1st May, 1845.