A. J. Downing, Esq. - Dear Sir: On the score of sound practice in agriculture, rather than of courtesy to me, I claim the privilege of saying a word in relation to the strictures in your last number, upon my remarks on " Green Crops as a Manure." I do not complain that you took occasion to animadvert upon anything thing you found worthy of noting in my Agricultural Address at Lancaster, being well aware that it was perfectly at your option to single out for comment, whatever you might deem objectionable. Acknowledging, also, that I have no right to expect every one should concur in my views, upon a matter as susceptible of a difference of opinion, as the condition of farms and the position of farmers differ - the circumstances being the rule by which to determine the necessity or propriety of turning in a crop to serve as manure.

In my address, in which the turning in of green crops was merely incidental, it could not be expected that the special cases, justifying a resort to such manuring, could be enumerated - I could but deal with the subject in a broad and general sense, and from a long and close observation on the practice of husbandry, a sense of duty constrained me to denounce the custom of raising crops to be plowed under, as " time wasting and land cheating." No one, not even 3'ourself, Mr. Editor, can have a higher appreciation of vegetable mold than I have, and I challenge New-Tork, or any farm in Pennsylvania, to show better sods on uplands, after having yielded for as many years, heavy crops of bay, than I can now show upon my place; and may safely add, that I am yet to meet the man who would rejoice more in having such a sod to turn under, when it becomes necessary to break it up; but with all this appreciation, I would not rely upon it to bring me a crop of grain, potatoes, Ac, without the addition of what is known among farmers as " barnyard manure," notwithstanding such a sod would be richer and more enduring than the " scant crops of partly grown clover, buckwheat, etc," which I pointed at as unworthy the name of manure.

Had these fields I hare mown for some seven or eight years, been laid down in 1833 and 4, with only clover or buckwheat, and the like, turned in, would they, as they did, have yielded forty to forty-five bushels of wheat to the acre, as first crops, and cut ever since close on two tons of fine hay, on an average, to the acre?

Assuredly not. In the course of two or three years at farthest, the crop of clover growing, would be required to turn under, to serve as manure for a grain or some other crop, involving prematurely the labor of breaking up, seeding, etc.; and what would be the condition of the land, and the character of the crops, after another two or three years shift under such a practice - I allude to such soils as we cultivate? It was in view of this system that I said, " in whatever place it is practiced, however strong the land may be at the 8tart, the system, if persevered in, must inevitably bring the land, its owners, and the country, into a state of poverty. No good husbandman would think of pursuing such a course".

If the address had been fairly read, its general bearing and scope properly considered, it might, perhaps, have saved you and others from drawing the inference, that I held clover and other green crops worthless as fertilizers. I never so thought, nor did I intend to be so understood. I knew clover would in some degree serve the purpose of manure, and so, would potatoes, wheat, rye, barley, etc. etc, but I knew also that these, as clover, would be costly and but indifferent manures, compared to barn yard manure, peat, and putrescent substances, which if not used to enrich the land, would become pestilential nuisances; for we must have cattle and other live stock - while offal and other offensive matter would be constantly accumulating. Insisting, as I did, upon the crops going to the barn, to be put to their proper use, and the offensive matters applied, as they should be, to the land; and in this, who shall be so unthinking as to say, I was wrong? Moreover, I had been grieved to perceive a germ of quackery springing up with our efforts at scientific agriculture, and while I attempted to awaken the good farmers of Lancaster to a proper spirit of improvement, I took occasion, husbandman like, to caution them against nostrums and humbug, urging a chief reliance upon the cheap and excellent manures so easily obtained in and about their barn yard and premises.

To the question whether I have seen the statement of Mr. More, in regard to his premium farm - I answer that I have; and, instead of condemning his practice, have simply to say, that had I been in his situation, I might, perhaps, have resorted to the same means, he had recourse to for the improvement of his land. But did Mr. More depend solely upon the turning in of green crops, pending the process of renovating it? I presume he used other manures, which with gypsum, aiding in restoring his farm to good condition. But this case, and and others I have heard of, do not affect the force of the injunction against a persevering system of turning in grain crops as a substitute for manure. It may be that this very land that Mr. Mori found so wretchedly impoverished, when he took possession of it, owed much of its poverty to his predecessor having followed more closely the appliances of clover, buckwheat, Ac., by way of manure than Mr. Mori did - one thing at least is certain, and that is, the impoverishment was not owing to the former owner or tenant having been too liberal in the application of barn yard manure.

Now the best way to test the soundness of my views, as to the syntem I so deprecated, would be, for some one having a farm in such good condition as Mr. Morr's is now found to be in, to follow the green crop system thoroughly for five years, discarding the vulgar practice, if you please, of husbanding barn yard and stable manure. To note the seasons consumed in raising the crops to be turned under, to produce the " carbon," " oxygen," "nitrogen," etc. - the simon pure fertilizers required to grow the wheat, rye, corn, potatoes, etc. etc, for the barn - to keep an exact account of the value of the crops so housed, together with the sum total of the expenses of the farm, and then to exhibit the net gain in the "yellow boys" that are now jingled in " Mr. Gowin's" ears, to convince him of the profits resulting from the turning in green crops instead of manure; and if such a system, on such a farm, at the end of five years, leaves the purse well filled and the land in as high condition as at the beginning, I shall not only confess that I was wrong, but be willing to pay a premium of half the value of the farm to the husbandman who had worked such a miracle.

Let it be rembered that it was such land, as this, not worn out land that I had in view, as may easily be perceived by my remarks, for how could the land be brought "into a state of poverty," that had not been rich, but in poverty already? If, Mr. Editor, you will take the trouble to again glance at the address, from which you have predicted that if I go on at the rate you infer I am going, I will, as you say, "demonstrate that there is no warmth begotten by sunshine," you will be led to believe at least, that I am in but little danger of dealing in moonshine. Your obedient servant, James Gowrn.

Mount Airy, Philadelphia, July 19th, 1852.