How does it prevent the escape of ammonia?
Sulphuric acid is a very important constituent of vegetable ashes, especially of oats and the root-crops.
It is often deficient in the soil, particularly where potatoes have been long cultivated. One of the reasons why plaster (sulphate of lime) is so beneficial to the potato crop is undoubtedly that it supplies it with sulphuric acid.
Sulphuric acid is commonly known by the name of oil vitriol, and may be purchased for agricultural purposes at a low price. It may be used in a very dilute form (weakened by mixing it with a large quantity of water) to the compost heap, where it will change the ammonia to a sulphate as soon as formed, and thus prevent its loss, as the sulphate of ammonia is not volatile; and, being soluble in water, is useful to plants. Some idea of the value of this compound may be formed from the fact that manufacturers of manures are willing to pay seven cents per lb., or even more, for sulphate of ammonia, to insure the success of their fertilizers. Notwithstanding this, many farmers persist in throwing away hundreds of pounds of ammonia every year, as a tax for their ignorance (or indolence), while a small tax in money—not more valuable, nor more necessary to their success—for the support of common schools, and the better education of the young, is too often unwillingly paid.
What is the effect of using too much sulphuric acid?
If a tumbler full of sulphuric acid (costing a few cents), be thrown into the tank of the compost heap once a month, the benefit to the manure would be very great.
Where a deficiency of sulphuric acid in the soil is indicated by analysis, it may be supplied in this way, or by the use of plaster or refuse epsom salts.
Care is necessary that too much sulphuric acid be not used, as it would prevent the proper decomposition of manures, and would induce a growth of sorrel in the soil by making it sour.
In many instances, it will be found profitable to use sulphuric acid in the manufacture of super-phosphate of lime (as directed under the head of 'phosphoric acid,') thus making it perform the double purpose of preparing an available form of phosphate, and of supplying sulphur and sulphuric acid to the plant.