It is stated that an acre of hay pumps up out of the soil 500 tons of water per annum, so it is easy to see what an important feature this natural water-storage is.
Farmers say that their crops have doubled in value after thus dynamiting the subsoil.
This operation has been spoken of as a substitute for ploughing, but that may be put down to "journalistic licence," for while it truly conveys the general idea, it is hardly correct. The ordinary plough turns over about eight inches, the special subsoil plough reaches down to about eighteen inches, but the dynamite method loosens the ground to a depth of six or seven feet. Corn roots if given a chance will go downwards from four to eight feet. Potatoes go down three feet, hops eight to eighteen feet and vines twenty feet, so it is easy to see how restricted the plants are when their natural rooting instincts are restrained by a hard layer at a depth of eighteen
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inches or so.
The holes are made by means of a bar or drill. A great deal depends, of course, upon the hardness of the soil. Sometimes a steel bar has to be driven in by a sledge-hammer. At others a pointed bar can be pushed down by hand. In some cases it will be found that the best tool to employ is a "dirt-auger," a tool like a carpenter's auger, which on being turned round and round bores its way into the earth. However it may be done, one or more cartridges of dynamite are lowered into the finished hole, one of them being fitted with the necessary detonator and fuse. Then a little loose earth or sand is dropped into the hole until it is filled to a depth of six inches or so above the uppermost cartridge. Above that it is quite safe to fill the hole with earth, ramming it in with a wooden rammer. This is called "tamping," and it is necessary in order to prevent the force of the explosion being wasted in simply blowing up the hole. What is wanted is that the explosion shall take place within an enclosed chamber so that its effect may be felt equally[16] in all directions. The holes are generally about an inch and a half or an inch and three-quarters in diameter.
There are two ways of firing the charges. One is by means of fuses. The detonator is fastened to one cartridge and a length of fuse is attached to the detonator, which passing up the hole terminates above the ground. The fuse is a tube of cotton filled with gunpowder, and it burns at the rate of about two feet a minute. Thus if three feet of fuse be used the man who lights it has a minute and a half in which to find a place of safety from falling stones.
The other way is by electricity. In this case an electric fuse is attached to the cartridge and two wires are led up the hole. These are connected to an electrical machine, which causes a current to pass down into the fuse, where, by heating a fine platinum wire, it fires the detonating material with which it is packed. This detonating material in turn fires the dynamite.
The advantage of the electrical method is that twenty or thirty holes being simultaneously connected to the same machine can all be
fired at once.
And now let us think of another kind of farming, in which fruit trees are concerned. With a large tree the need of plenty of underground space for its roots would seem to be more important even than in the case of annual plants like wheat. Yet we know very
well that the usual procedure is to dig a small hole just about big enough to accommodate the roots of the sapling when it is planted, while the ground all round is left undisturbed. The assumption is that the tree will, in time, be able to push its roots through anything which is not actually solid rock. So much is this the case that one authority has thought fit to warn tree-growers in this picturesque fashion. "When planting a tree," he says, "forget what it is you are doing, and think that you are about to bury the biggest horse you know." How many people when planting any tree dig a hole big enough to bury a horse? It is fairly safe to reply, only those who do it by dynamite.
By permission of Dupont Powder Co., Wilmington, Delaware
First Effect of the Dynamite
Clearing a field of tree stumps by blowing them up with dynamite.--See p. 16
[17]
The method of working is to bore a hole nearly as deep as the hole you want to blast. At the bottom place a powerful charge, far stronger than you would use for "subsoiling," as just described. That will not only blow a hole big enough for you to put your tree in, but it will loosen the ground all around the hole for yards. The main debris from the hole will fall back into it, but that will not
matter much, since, being all loose, it is an easy matter to remove as much as is necessary to plant the young tree. The advantages are the same as those enumerated in the previous case--namely, the loosened ground gives more scope for the roots--apple-tree roots want twenty feet or so--the ground holds moisture better, and the explosion kills the fungus germs. In addition to these there is the advantage that to blast a hole like this is cheaper than digging it.
And that the advantages are not merely theoretical is shown by the fact that trees so planted actually do grow stronger, bigger and quicker than precisely similar ones under the same conditions, but set in the ordinary way with a spade.
And not only do new trees thus benefit; old trees can be helped by dynamite. Many an existing orchard has been improved by exploding dynamite at intervals between the rows of trees. Care has to be taken to see that the disturbance is not so violent or so close as to damage the trees, but that can be easily arranged, and then the result is that the soil all around the trees is loosened, the roots are given more freedom and the water-storing properties of the ground are greatly improved.
Again, how often a farmer is troubled with a pond or a patch of marshy ground right in the midst of his fields. It is of no use,
and simply serves to make the field in which it occurs more difficult to plough and to cultivate--besides being so much good land wasted. Now the reason for the existence of that pond or marsh is that underneath the surface there is an impervious layer in which, as in a basin, the water can collect. Make a hole in that and it will no[18] more hold water than a cracked jug will. And to make that
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hole with dynamite is the easiest thing in the world.
If the pond be merely a collection of water which occurs in wet weather, but which dries up quickly, there simply needs to be drilled a deep hole and a fairly strong explosion caused at the bottom of it. How deep the hole must be depends upon the formation of the earth at that point, and how low down is the stratum which, being waterproof, causes the water to remain. It is that, of course, which must be broken through, and so the explosion must be caused at a point near the under side of that layer. With a little experience
the operator can judge the position by the feel of the tool with which he makes the hole. If the pond is permanent but shallow, men can wade to about the centre, there to drill a hole and fire a shot. If it be permanent and deep, then the work must be done from a raft, which, however, can be easily constructed for the purpose. Once broken through, the water will quickly pass away below the impervious stratum and useless land will become valuable.
The same may be done on a larger scale by blasting ditches with dynamite. This is in many cases much cheaper than digging them. A row of holes is put down, or even two or three rows, according to the width of the proposed ditch. In depth they are made a lit-tle less than the depth of the ditch that is to be. And for a reason which will be apparent they are put very close together, say three feet or so apart. Preparations may thus be made for blasting a ditch hundreds of feet long and then all are fired together. The earth is thrown up by a mighty upheaval, a ditch being produced of remarkable regularity considering the means by which it is made.
The sides, of course, take a nice slope, the debris is thrown away on both sides and spread to a considerable distance, so that, given favourable conditions and a well-arranged explosion, there is constructed a finished ditch which hardly needs touching with spade or other tool.
It not being feasible to fire a lot of holes electrically, the limit being about thirty, the simultaneous explosion of[19] perhaps hundreds has to be brought about in some other manner, and usually it is accomplished by the simple device of putting the holes fairly near together and firing one with a fuse. The commotion set up by this one causes the nearest ones to