"You will readily perceive, therefore, that the sulphuric and phosphoric acids require amendments, and the ammonia should be changed from a carbonate to a sulphate of ammonia, which is not volatile. All this may be readily done by dissolving bone dust in dilute sulphuric acid, mixing it with the guano, and then with a sufficient amount of charcoal dust to render the mass dry and pulverulent. The more charcoal dust the better, as it absorbs and retains ammonia, and after it is in the soil, will continue to perform similar offices for many years, only yielding up ammonia as required by plants, and receiving new portions from rains, dews, &c."
If used as a top dressing, this change from a carbonate to a sulphate may be necessary; but not so if well mixed with the soil, particularly one in which clay predominates. In such a soil it is not even necessary to adhere to the direction to plow the guano deeply under. If it is but slightly harrowed in, the nature of the clay is such it will prevent the escape of the ammonia. If you require phosphates, more than ammonia, add the superphosphate of lime; but in no case omit the guano.
_Use of Salt with Guano._--Common salt at the rate of a bushel to 100 lbs. of guano, well mixed, may be used to good advantage either as a top dressing, or when plowed in. The effect of the muriatic acid of the salt upon the guano will be, as both are dissolved in the earth, or by dews and rains, to form muriate of ammonia, which is not volatile; consequently the salt prevents loss by exhaustion, which is sure to take place when the guano is used as a top dressing, unless prevented by something to act as a fixer of the ammonia.
The wisdom of this law of nature in making the most precious saline manure a fixed and difficultly soluble salt, is at once obvious; for it is thus kept always ready in the soil for the plants to act upon according to their need. If we cut plants down before the seeds form, we have all the phosphates the plants contain diffused throughout them, and if we allow the seed to ripen, the phosphates, as before observed, will be found mostly in the seed. We find them in the state of phosphate of potash, phosphate of soda, phosphate of magnesia, and phosphate of lime, and probably, also, phosphate of ammonia. Now all these salts are essential to the growth and sustenance of animals, and without them grain would cease to be sufficient.