Gardeners generally prepare their soils, so far as my observation has extended, in a very practical way, with little or no attention to the chemical principles involved in the operation. 'They have learned, by long experience, that a partially rotted sod makes the best general soil that can be obtained. Farmers know that a clover sod plowed under makes good manuring for corn; but farmers seldom, f ever, make a compost of sods for their gardens or manure heaps. Gardeners are clearly ahead of farmers in their method of cultivation and fertilization, but they are by no means up to the standard of modern science in their preparation and management of soils.

How to rot or decompose a heap of sods, has long been the study of gardeners. Some let it lie in a heap, with occasional turnings and choppings, for two or three years. Others, finding that the use of lime and the access of air hastened decay, put up the heap with lime, and used sticks or pieces of timber to separate the mass and admit air. Others tried the addition of heating dung and water.

Now all these methods are slow and imperfect That they are slow and tedious, all who have tried them well know; that they are imperfect, I will endeavor to prove.

It is well known that plants can receive nutriment only in the form of a fluid or a gas. No solid particles of matter, of any description, can enter the circulation of plants. Hence, everything intended for their use must be capable of being dissolved in water, or of being converted into a gas, when needed. Now if a sod, though rich in fertilizing materials, be not completely rotted or decomposed, or in a state to become fully rotted and decomposed, it follows that its constituents can not possibly become immediately useful. Clover contains many valuable fertilizing ingredients; but until these ingredients become changed from the form of clover into their chemical elements, (lime, potash, soda, etc.,) they can not be appropriated by plants. Again, even if the clover be decomposed, and the chemical elements remain in such relations that they are insoluble in water, or not capable of readily becoming gases, they can not be made available in the garden. Of course it will be seen at once that under such circumstances a gardener may have a heap of rich material, and yet, if it is not available, it is no better for present use than a poor heap.

The imperfection of the process commonly adopted in composting garden soils consists in several points. First, where all the soil is fresh, there is no well decomposed matter of a carbonaceous character to act as an absorbent of the gases generated by the act of decomposition, and hence much valuable material (ammonia) is lost. In all such compost heaps a quantity of well decomposed turf or black, garden soil should be mixed with the new soil, to catch the ammonia produced by the decay of the new soil or sod. Again, much valuable time and labor is lost by the slow decay of sod where no chemical agent is employed to assist the decomposition. Lime is an objectionable agent, because, when freely used, it locks up nearly as much fertilizing material as it liberates. Stable manure, in a state of rapid decay, or high heat, is not so objectionable as lime; but this is not the best material for this purpose. Water in moderate quantities is highly important; but with this should be used potash - the common potash of the shops - which decomposes all vegetable matter rapidly and powerfully, and does not lock it up in new combinations as lime does, but on the contrary sets free even those combinations which lime renders insoluble.

With solutions of potash in water, any heap of sod or other vegetable matter may be decomposed as rapidly as the operator may desire, and all the constituents of the heap will be placed in a state easily soluble in water, or ready to become gases, on the slightest action of water and vegetable life. Indeed, the ingredients of plants are by potash converted in great measure into gases; and if there be present vegetable charcoal, (black loam,) or animal charcoal, (bone black,) or clay, these gases will be caught up and retained till taken up by plants. No organized vegetable body can resist the action of potash; it must decay, and resolve itself into its original elements at its touch. In fact, it is not necessary that the potash should touch the substance of the vegetable; it acts by its mere presence in a near part of the heap, disposing not only that matter which it touches, but all other matter in contact with that which it affects, to decay. "Rot makes rot," is an old adage; and so it is in an especial manner with the rot caused by potash.

All who undertake the cultivation of the earth, either in the field or the garden, should bear in mind these important principles. You may have rich fields, but their riches may not be available to plants. Ashes or potash may be highly important to bring your peat, turf, meadow mud, raw coarse manure, sod heaps, etc., into efficient action. Lime is useful in small quantities, and so is salt; but I consider large quantities of lime dangerous for many reasons beside that mentioned above. Potash is worth its cost as a manure independent of its power as a decomposing agent, and in garden work it is indispensable. Applied in solution, in free quantities of water, it will bring a sod heap into a better state in sixty days than two years of rotting and turning will effect by the old methods without it.

[This question concerning the management of composts is one in which we have personally a very great interest, some thousands of loads being made annually on our premises. It is a question, too, full of importance to every cultivator; for no matter what our soil be, or where we live, or what we cultivate - whether it be wheat, or corn, or potatoes, or trees, or shrubs, or flowers - fertilizing composts we most have, and that in abundance, as we hope for successful and profitable results.

We have never used potash, but we have not a doubt of its efficacy or of its value, especially where fresh materials are to be brought speedily into a fit condition for use.

We always aim at having our composts at least a year old. They are made up of alternate layers of stable manure, fresh sods from end lands, swamp muck, leaves, street cleanings, weeds, an occasional sprinkling of lime, and everything, we believe, but stones. The heap is subjected to several turnings and mixings during the season, so that when we haul it out for use it is a soft pasty mold.

We shall be glad to have this subject thoroughly discussed in our columns, both by practical and scientific men.