British writers say that lime may be applied with equal advantage either when newly slaked or afterwards, that its effects are not always the same particularly where soils are different, but that usually it is a very durable manure. A much larger quantity is, however, applied in Great Britain than has been usual here; but perhaps the coolness of the summers there renders more requisite. We pretend to advise to no particular rules in the application of lime in this country, farther than that about forty bushels to the acre be first tried; but less for sandy soils, and perhaps more for those which are stiff clays would be advisable. In clays of this description, lime is particularly useful in destroying the adhesive quality of such soils, and thereby rendering them a more friable loam. Such has been its effects on the clay lands which abound so much in England. Where the lime is magnesian, let trials be made of about twenty bushels to the acre.
That country abounds much in the calcareous matter denominated chalk, which is also converted into lime by calcination, and used as a manure. It forms a weaker sort of lime. As this substance, however, is hardly to be found in this country, it will be unnecessary further to speak of this manure.
Gypsum, (sulphate of lime) is a most powerful stimulant to the growth of many crops in all dry soils in this country, but with the following exceptions: it has no sensible effect on lands newly cleared, on those in the vicinity of the ocean, nor on those which have been completely exhausted by severe cropping. In soils of this latter description, some pabulous matter must be given them for the gypsum to digest or act upon; and this may be a previous manuring with lime, marl, bog-earth, barn dung, or perhaps any substance that is calculated to improve the condition of the soil. It should also be observed that the application of gypsum frequently fails entirely of producing its effects if followed by uncommon drought, or unusually wet weather. It is generally most powerful when applied to growths of leguminous plants, to those extending in vines, such as the various species of the gourd tribe, the strawberry, &c. and to several sorts of the green crops, particularly potatoes, clover-grasses, lucern, &c. On fibrous rooted grasses, and those grain plants most nearly related to them, such as wheat, rye, oats, barley, &c. it has no sensible effect when applied as a top dressing to the growing plants. On Buckwheat it is very powerful, and for Indian corn it is also valuable. Judge Peters, (of Penn.) whose experience of its uses has been long and extensive, says that although he has found this manure of little use to many sorts of plants, when applied to them as a top dressing, yet he has invariably found that all plants derive benefit from their seeds being rolled in gypsum, after being soaked in some liquid, before sowing or planting. As a manure, however, for wheat or grain crops of similar kinds, immense benefit may be derived from it by applying it to the sward, as a top dressing, a suitable length of time before the ground is broken up. In this way two bushels of gypsum may be made to give an additional increase of eight or ten bushels of wheat to the acre. Take, for instance, land which in its natural state, and with the usual culture, will only yield ten bushels of wheat to the acre; in the fall or early in the spring, give it a top dressing of two bushels of gypsum to the acre; by the middle of June following, the land will exhibit a fresh green sward, principally of white clover; and when land is thus clothed in verdure, it is a sure indication of a great addition to its fertility, and that a good crop may then be expected. When, therefore, the green sward is thus formed, turn it under, and then, with the usual culture, twenty bushels of wheat to the acre may be expected, where only ten would have been had without this previous enriching of the ground by the application of gypsum. Yet the same quantity of this manure, applied as a top dressing to the growing crop of wheat, would have had no sensible effect. It should therefore be understood, that for all growths which derive little or no benefit from gypsum, when applied as a top dressing to the growing plants, the ground should be previously enriched by applying this manure to the sward, a suitable length of time before it is to be broken up, which length of time will usually be from two to three months. At all events as soon as the sward fully exhibits the effects of the gypsum it may then be turned under. Wherever a sward is to be turned under, this practice should be invariably pursued in order that the ground be rendered more fruitful for the crop that is to follow.