The Elements of Agriculture Part 21

GREEN CROPS.

[What plants are most used as green crops?

What office is performed by the roots of green crops?

How do such manures increase the organic matter of soils?]

_Green crops_, to plow under, are in many places largely raised, and are always beneficial. The plants most used for this purpose, in our country, are clover, buckwheat, and peas. These plants have very long roots, which they send deep in the soil, to draw up mineral matter for their support. This mineral matter is deposited in the plant. The leaves and roots receive carbonic acid and ammonia from the air, and from water. In this manner they obtain their carbon. When the crop is turned under the soil, it decomposes, and the carbon, as well as the mineral ingredients obtained from the subsoil, are deposited in the surface soil, and become of use to succeeding crops. The hollow stalks of the buckwheat and pea, serve as tubes, in the soil, for the pa.s.sage of air, and thus, in heavy soils, give a much needed circulation of atmospheric fertilizers.

[What office is performed by the straw of the buckwheat and pea?

What treatment may be subst.i.tuted for the use of green crops?

Which course should be adopted in high farming?

Why is the use of green crops preferable in ordinary cultivation?

Name some other valuable manures.]

Although green crops are of great benefit, and are managed with little labor, there is no doubt but the same results may be more economically produced. A few loads of prepared muck will do more towards increasing the organic matter in the soil, than a very heavy crop of clover, while it would be ready for immediate cultivation, instead of having to lie idle during the year required in the production and decomposition of the green crop. The effect of the roots penetrating the subsoil is, as we have seen, to draw up inorganic matter, to be deposited within reach of the roots of future crops. In the next section we shall show that this end may be much more efficiently attained by the use of the sub-soil plow, which makes a pa.s.sage for the roots into the subsoil, where they can obtain for themselves what would, in the other case, be brought up for them by the roots of the green crop.

The offices of the hollow straws may be performed by a system of ridging and back furrowing, having previously covered the soil with leaves, or other refuse organic material.

In _high farming_, where the object of the cultivator is to make a profitable investment of labor, these last named methods will be found most expedient; but, if the farmer have a large quant.i.ty of land, and can afford but a limited amount of labor, the raising of green crops, to be plowed under in the fall, will probably be adopted.

Before closing this chapter, it may be well to remark that there are various other fertilizers, such as the _ammoniacal liquor of gas-houses_, _soapers' wastes_, _bleachers' lye_, _lees of old oil casks, etc._, which we have not s.p.a.ce to consider at length, but which are all valuable as additions to the compost heap, or as applications, in a liquid form, to the soil.

[What are the advantages arising from burying manure in its green state?

Which is generally preferable, this course, or composting? Why?]

In many cases (when heavy manuring is practised), it may be well to apply organic manures to the soil in a green state, turn them under, and allow them to undergo decomposition in the ground. The advantages of this system are, that the _heat_, resulting from the chemical changes, will hasten the growth of plants, by making the soil warmer; the carbonic acid formed will be presented to the roots instead of escaping into the atmosphere; and if the soil be heavy, the rising of the gases will tend to loosen it, and the leaving vacant of the s.p.a.ces occupied by the solid matters will, on their being resolved into gases, render the soil of a more porous character. As a general rule, however, in ordinary farming, where the amount of manure applied is only sufficient for the supply of food to the crop, it is undoubtedly better to have it previously decomposed--_cooked_ as it were, for the uses of the plants--as they can then obtain the required amount of nutriment as fast as needed.

ABSORPTION OF MOISTURE.

It is often convenient to know the relative power of different manures to absorb moisture from the atmosphere, especially when we wish to manure lands that suffer from drought. The following results are given by C. W. Johnson, in his essay on salt, (pp. 8 and 19). In these experiments the animal manures were employed without any admixture of straw.

PARTS 1000 parts of horse dung, dried in a temperature of 100, absorbed by exposure for three hours, to air saturated with moisture, of the temperature of 62 145 1000 parts of cow dung, under the same circ.u.mstances, absorbed 130 1000 parts pig dung 120 1000 " sheep " 81 1000 " pigeon " 50 1000 " rich alluvial soil 14 1000 " fresh tanner's bark 115 1000 " putrified " 145 1000 " refuse marine salt sold as manure 49 1000 " soot 36 1000 " burnt clay 29 1000 " coal ashes 14 1000 " lime 11 1000 " sediment from salt pans 10 1000 " crushed rock salt 10 1000 " gypsum 9 1000 " salt 4[AE]

Muck is a most excellent absorbent of moisture, when thoroughly decomposed.

DISTRIBUTION OF MANURES.

The following table from Johnson, on manures, will be found convenient in the distribution of manures.

By its a.s.sistance the farmer will know how many loads of manure he requires, dividing each load into a stated number of heaps, and placing them at certain distances. In this manner manure may be applied evenly, and calculation may be made as to the amount, per acre, which a certain quant.i.ty will supply.[AF]

----------+----------------------------------------------------------- DISTANCE OF THE HEAPS. NUMBER OF HEAPS IN A LOAD.

----------+-----+-----+-----+-----+-----+-----+-----+-----+-----+----- 1 2 3 4 5 6 7 8 9 10 ----------+-----+-----+-----+-----+-----+-----+-----+-----+-----+----- 3 yards. 538 269 179 134 108 89 77 67 60 54 3 do. 395 168 132 99 79 66 56 49 44 39 4 do. 303 151 101 75 60 50 43 37 33 30 4 do. 239 120 79 60 47 39 34 30 26 24 5 do. 194 97 64 48 38 32 27 24 21 19 5 do. 160 80 53 40 32 26 22 20 17 16 6 do. 131 67 44 33 27 22 19 16 15 13 6 do. 115 57 38 28 23 19 16 14 12 11 7 do. 99 49 33 24 19 16 14 12 11 10 7 do. 86 43 28 21 17 14 12 10 9 8 8 do. 75 37 25 19 15 12 10 9 8 7 8 do. 67 33 22 16 13 11 9 8 7 6 9 do. 60 30 20 15 12 10 8 7 6 6 9 do. 53 26 18 13 10 9 7 6 6 5 10 do. 48 24 16 12 9 8 7 6 5 4 ----------+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----

_Example 1._--Required, the number of loads necessary to manure an acre of ground, dividing each load into six heaps, and placing them at a distance of 4 yards from each other? The answer by the table is 39.

_Example 2._--A farmer has a field containing 5 acres, over which he wishes to spread 82 loads of dung. Now 82 divided by 5, gives 15 loads per acre; and by referring to the table, it will be seen that the desired object may be accomplished, by making 4 heaps of a load, and placing them 9 yards apart, or by 9 heaps at 6 yards, as may be thought advisable.

FOOTNOTES:

[AC] Under some circ.u.mstances, _nitric acid_ is formed, which is equally beneficial to vegetable growth.

[AD] See the glossary at the end of the book.

[AE] Working Farmer, vol. 1, p. 55.

[AF] It is not necessary that this and the foregoing table should be learned by the scholar, but they will be found valuable for reference by the farmer.

CHAPTER VIII.

MINERAL MANURES.

[How many kinds of action have inorganic manures?

What is the first of these? The second? Third? Fourth?

Do all mineral manures possess all of these qualities?]

The second cla.s.s of manures named in the general division of the subject, in the early part of this chapter, comprises those of a mineral character, or _inorganic_ manures.

These manures have four kinds of action when applied to the soil.

1st. They furnish food for the inorganic part of plants.

2d. They prepare matters already in the soil, for a.s.similation by roots.

3d. They improve the mechanical condition of the soil.

4th. They absorb ammonia.

Some of the mineral manures produce in the soil only one of these effects, and others are efficient in two or all of them.

The principles to be considered in the use of mineral manures are essentially given in the first two sections of this book. It may be well, however, to repeat them briefly in this connection, and to give the _reasons_ why any of these manures are needed, from which we may learn what rules are to be observed in their application.

[Relate what you know of the properties of vegetable ashes?

How does this relate to the fertility of the soil?