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.