44G 
JOURNAL OF HORTICULTURE AND COTTAGE GARDENER. 
[ June !, 1887. 
second paragraph of Mr. Gilmour’s communication we are favoured with 
some elaborate calculations to show that I conclude (which I do not) 
^ that in eighty-nine years all the soluble silica will be gone, except we 
replace it.” Assuming the current crop to remove the 1^ per cent, of 
soluble silica, whence (I again ask) does the succeeding crop derive its 
supplies of soluble silica ? None in a soluble form is returned to the 
soil upon the lines pursued by the gentleman growing corn “ crop after 
■crop,” and yet we are asked to believe the supply of soluble silica 
abundant; indeed “ silica is abundant in all soils,” states Mr. Gilmour, 
quoting Johnston, but there is a great difference between soluble 
(l.j per cent.), and insoluble (70 or more per cent.). I asked (page 339) 
what is the value to the current crop of the 72, 69, and 77 per cent, of 
■silica ? For reply, we are told that silica, anywise the “ inorganic 
substances on which plants live,” are derived from minerals and rocks 
decomposed under the conjoined action of the exygen, the carbonic acid, 
and the moisture of the atmosphere. (Johnston). “ There is the rub.” 
The “ fragments of felspar and other minerals dirived from the granitic 
and trap rocks, slaty, and other beds, are of no use productively through 
their insolubility, until brought under the “ conjoined action of the 
exygen, the carbonic acid, and the moisture of the atmosphere.” Who 
in these days practises trenching and subsoiling ? Who, indeed, cares to 
do more than “tickle the surface?” Yet Mr. Gilmour asks us to see 
what “ a store of silica we have in the soil to gradually become soluble.” 
Nature is lavish ; silicon, after oxygen, is the most abundant of the 
elements, forming about 29.j per cent, of the earth’s crust. 
Let us take a closer view of silica (oxide and acid of silicon, or 
silicon dioxide). Consider it as the anhydride of an acid and we get 
silicic acid or a compound of silicic anhydride with water, just as nitric 
acid is considered as a compound of nitric anhydride with water. 
Hydrogen silicates are obtained by the union with water, and a similar 
decomposition is effected by carbon, and these are soluble by potassium 
and sodium hydroxides forming corresponding silicates. The silicates 
(hydrogen and carbon) are also more or less soluble in (what Mr. 
Gilmour scrupulously avoids naming) ammonia, and in many acids. An 
analogous decomposition is constantly going on in Nature, causing the 
disintegration of rocks composed of metallic silicates. 
Silica is rendered soluble naturally, and the supplies are increased 
by manuring, and breaking the surface soil inseparable from cultivation. 
■“ That is what I contend for,” Mr. Gilmour may say, which I readily 
grant represents his case ; but I contend that silica is inseparable from 
animal manure, and that it is not applied to any soil, and especially 
clay, without contributing through its soluble silica to the greater 
advantage of the current and succeeding crops than artificials, which, 
if they do contain soluble silica, the quantity is infinitessimal. In that 
sense, and that only, do I advise the application of farmyard manure, 
and in that— i.e., its soluble silica —I see its greater benefit to the cul¬ 
tivator. Who thought of separating all the phosphates, nitrates, Ac., 
from farmyard manure, and giving those to Mr. Gilmour ? The illus¬ 
tration is far-fetched and unreasonable. Cultivators need all the ferti¬ 
lising properties of farmyard manure, and have no cause to waste any, 
not even the silica, which Mr. Gilmour would have us believe valueless. 
If so, why have it in the soil? Lampadius formed the opinion that the 
earths contained in plants were merely the effects of vegetation, and 
altogether independent of the soil in which they grow. The experi¬ 
ment was as follows :—Five beds, 4 feet square by 1 foot in depth, each 
containing a pure earth—-alumina, sdica, lime, magnesia, garden mould, 
and each mixed with 8 lbs. of cowdung—were sown with Rye. The 
produce of each was separately reduced to ashes, and the same principles 
were found in them all, particularly a portion of silica. Whence came 
the silica in the bed of alumina? According to Lampadius it was the 
Tesult of vegetation. But Saussure, like Ruckert, has shown that 
cowdung contains a portion of silica. Hence the substance which 
Lampadius could not account for but by means of vegetation he had 
supplied with his own hands. It is now known that the earths are 
partially soluble, some of them in pure water, and all of them with the 
aid of acids (“ Science and Practice of Gardening,” pages 81 and 82). 
This is evidence that silica is restored to the soil in farmyard manure. 
I must also take exception to Mr. Gilmour indulging in a little 
sarcasm (albeit at his own expense) in respect of carting silica sixteen 
miles. Admitting Mr. Gilmour’s fancy calculations in respect of the 
silica removed in hay, I fail to see that it has any correlation or analogy 
in respect of the silica in farmyard manure. There surely is a difference 
between sixteen loads of farmyard manure and a like quantity of road 
scrapings, for who is such a dolt as not to know the manurial value 
of the two substances ? Sand is conveyed many miles to make mortar 
to build houses on the London clay, and manure is brought not only 
sixteen miles into Herts to grow hay, but over fifty to enrich the silicious 
soil of Beds and Hunts, for the growth of vegetables. “ Ah 1 the silica is 
of no use,” Mr. Gilmour may say in triumph, but I wish to know how it is 
that farmyard manure, guano, and soot exhibit in the crops more per¬ 
manently sustained values over the silicates of artificials with their 
infinitessimal phosphates, and nitrates thrown in ? But really, who can 
follow Mr .Gilmour’s argument ? In his first communication he stated 
I attributed the value of farmyard manure to its silica,and in his second 
he states I credit it to the “acids in the manure.” Who would cart 
farmyard manure sixteen miles, or pa? the carriage for twelve tons of 
manure over fifty miles, when we can get as much silica as is needed for 
two loads of hay in 300 lbs., or as much value from a few cwt. of arti¬ 
ficials 1 Surely gardeners and farmers are not so stupid. 
Then Mr. Gilmour fails to see how manuring grass land is as valuable 
jom a hay-producing point of view in the second as in the first year 
after manuring, which is to say the least an admittance on his part of 
inexperience in the application of solid manures. Granted the most 
value from the manure is wanted the first year in a hay crop, when 
would the application best be made ? In autumn or in spring? If in 
autumn the manurial matter would be washed away by rains, therefore 
the hay crop following would derive correspondingly less benefit. Do 
not misunderstand me, I am following Mr. Gilmour. The contrary is the 
fact—autumn manuring meaning an early and thick growth of grass, 
and of a higher market and nutritive value than the results of spring 
manuring. If Mr. Gilmour is dubious let him examine any meadow 
manured in spring, and he may see large tufts of grass much in advance 
of the other, and from the places where the dung has been dropped in 
autumn. The rain has not washed it away but into the soil—alumina 
has retained the “soluble portion of the manure,” especially “ ammonia,” 
which, as before stated, dissolves silica, therefore we get from an autumn 
manuring a higher quality hay than results of a spring application. For 
a supply of the market we need two kinds of hay—viz., short and soft 
for cows, and long and hard for horses. The difference in the values is 
considerable, from a growing point of view vital. By manuring in 
autumn or after the hay crop we secure a strong aftermath, and as this 
admits of more stock the ground is enriched by the manure directly 
returned to the soil as well as that given previously, which requires time 
to act and attack the mineral constituents, thereby inducing a greater 
disposition on the part of the plants to the production of seed than 
attends a spring manuring, with acceleration of the coarser and least 
nutritive grasses. So with the manuring in alternate years—a vigorous 
growth the first year, a strong aftermath and a thick growth the second. 
Id that way grass land continues to yield excellent hay crops year after 
year, the whole, if not more, of the silica removed being restored to the 
soil, for, according to Mr. Gilmour, silica is of no value to man or 
animals except in the production of hair. He may well “ not doubt 
that farmyard manure will keep land, in good heart,” but I go beyond 
that and alarm that it improves it, just as Nature is progressive rather 
than retrograde. In all cases of progression it is when silica is restored 
to the soil, of which I shall only name an example, and it is that of grass 
land under permanent pasture, where the whole of the silica is returned 
directly to the soil, “ feeding ” matter enhancing the value of the 
manure as disintegrating mineral matter. 
There is another matter in the fourth paragraph of our friend’s 
communication that cannot be passed without observation. It is, 
“ What is the value of silica alone ? ” He is kind enough to answer 
the question—viz., “ silica in the ground acts as drainage, or combines 
and holds other more valuable constituents, as potash and lime, &c.,” 
but it is of no use to animals, “ they reject the whole of it.” Is he not 
aware of its sanitary as well as nutritive value? In observing the 
doings of fowls I am amused at nothing so much as their frequenting 
the sand heap. But it is surely valuable to fowls, and the “authorities ” 
tell how much soluble silica fowl manure contains, and which in all 
natural manures is proportionate to the ammonia. Let us return 
to the second paragraph of the criticism, where I find a not very 
complimentary allusion to road scrapings. I fear Mr. Gilmour has no 
experience of a clay soil, or he would have been aware of the potency of 
that material in making the soil porous, therefore favouring the absorp¬ 
tion of ammonia and the decomposition resulting of the “ conjoined 
action of the oxygen, the carbonic acid, and the moisture of the atmo¬ 
sphere,” by insuring their greater freedom in attacking stubborn 
material. Mr. Gilmour may object—it has no relation to grass land. 
Very well. Let us apply it to grass. I have in view a field from which 
hay is taken year after year. The land has no manure except that 
resulting from the eating of the aftermath by cattle, or none that 
contains silica in any appreciable quantity. Now parts of this parti¬ 
cular field are mossy and thin of grass, particularly Clover; in other 
parts it contains fair herbage with little or no moss. This field is dressed 
with road scrapings or sidings. I need not tell your readers that the 
best crop of hay is had from the ground dressed, and that the moss and 
bents prevail on the undressed. 
Mr. Gilmour’s explanation of using solid manure instead of artificial 
is singularly suggestive. His soil is sandy, and yet he adds more silica 
in a ton of manure than in a ton of artificial. This is remarkable reason¬ 
ing, but as Mr. Gilmour does not believe in sand (he is a greater advocate 
of organic manure than I am) we can hardly expect him to look on 
alumina with favour. Nevertheless, it would be a most valuable 
addition to a sandy soil, indeed to a sandy soil only capable of growing 
Rye I have known a dressing of clay result in 60 bushels of Wheat per 
acre. I am thankful to know that he has no intention of making 
experiments with artificials on ground “ made fertile with farmyard 
manure.” It struck me forcibly that experiment# conducted on such 
lines must be misleading, which is my apology for exceeding, as he 
insinuates, the limits of fair criticism. Injustice I have to admit that 
I did not intend to convey the impression that farmyard manure was 
valuable simply because of its soluble silica and silica-dissolving acids,” 
but for reasons given on page 339 I advised it in preference to artificials, 
and by that I am content to abide. The authorities I know are “ dead” 
on silicates, and this after careful experiment by Mr. Lawes and others ; 
but none of the authorities to which I have access have any fault to 
find with the silica as it obtains in any form of animal or vegetable 
manure, all admitting the great advantages of its employment and 
seeking b? all the means science dictates to prevent its waste. Were the 
“ authorities ” more strictly followed we should see more covered yards, 
less manure in heaps having its virtue washed out by rain, and more hay 
1 to cut along with more and bigger corn stacks. If our little discussion 
