As to whether it is better, when you can buy nitrogen at the same price in nitrate of soda as you can in sulphate of ammonia, to use the one or the other will depend on circumstances. The nitrogen exists as nitric acid in the nitrate of soda, and as ammonia in the sulphate of ammonia. But there are good reasons to believe that before ammonia is used by the plants it is converted into nitric acid. If, therefore, we could apply the nitrate just where it is wanted by the growing crop, and when there is rain enough to thoroughly distribute it through the soil to the depth of six or eight inches, there can be little doubt that the nitrate, in proportion to the nitrogen, would have a quicker and better effect than the sulphate of ammonia.
“There is another point to be considered,” said the Doctor. “Nitric acid is much more easily washed out of the soil than ammonia. More or less of the ammonia enters into chemical combination with portions of the soil, and may be retained for months or years.”
When we use nitrate of soda, we run the risk of losing more or less of it from leaching, while if we use ammonia, we lose, for the time being, more or less of it from its becoming locked up in insoluble combinations in the soil. For spring crops, such as barley or oats, or spring wheat, or for a meadow or lawn, or for top-dressing winter-wheat in the spring, the nitrate of soda, provided it is sown early enough, or at any time in the spring, just previous to a heavy rain, is likely to produce a better effect than the sulphate of ammonia. But for sowing in the autumn on winter-wheat the ammonia is to be preferred.
“Saltpetre, or nitrate of potash,” said the Deacon, “does not contain as much nitrogen as nitrate of soda.”
“And yet,” said the Doctor, “if it could be purchased at the same price, it would be the cheaper manure. It contains 46½ per cent of potash, and on soils, or for crops where potash is needed, we may sometimes be able to purchase saltpetre to advantage.”
“If I could come across a lot of damaged saltpetre,” said I, “that could be got for what it is worth as manure, I should like to try it on my apple trees—one row with nitrate of soda, and one row with nitrate of potash. When we apply manure to apple trees, the ammonia, phosphoric acid, and potash, are largely retained in the first few inches of surface soil, and the deeper roots get hold of only those portions which leach through the upper layer of earth. Nitric acid, however, is easily washed down into the subsoil, and would soon reach all the roots of the trees.”
[CHAPTER XXXVII.]
BONE-DUST AND SUPERPHOSPHATE OF LIME.
Bone-dust is often spoken of as a phosphatic manure, and it has been supposed that the astonishing effect bone-dust sometimes produces on old pasture-land, is due to its furnishing phosphoric acid to the soil.