"I wish," said the Deacon, "you would tell us something about the 'ammonia-salts' and nitrate of soda so long used in Lawes and Gilbert's experiments. I have never seen any of them."

"You could not invest a little money to better advantage than to send for a few bags of sulphate of ammonia and nitrate of soda. You would then see what they are, and would learn more by using them, than I can tell you in a month. You use them just as you would common salt. As a rule, the better plan is to sow them broadcast, and it is important to distribute them evenly. In sowing common salt, if you drop a handful in a place, it will kill the plants. And so it is with nitrate of soda or sulphate of ammonia. Two or three pounds on a square rod will do good, but if you put half of it on a square yard, it will burn up the crop, and the other half will be applied in such a small quant.i.ty that you will see but little effect, and will conclude that it is a humbug.

Judging from over thirty years' experience, I am safe in saying that not one man in ten can be trusted to sow these manures. They should be sown with as much care as you sow gra.s.s or clover-seed."

"The best plan," said the Doctor, "is to mix them with sifted coal-ashes, or with gypsum, or sifted earth."

"Perhaps so," said I, "though there is nothing gained by mixing earth or ashes with them, except in securing a more even distribution. And if I was going to sow them myself, I would much prefer sowing them unmixed.

Any man who can sow wheat or barley can sow sulphate of ammonia or nitrate of soda."

"Lawes and Gilbert," said the Deacon, "used sulphate and muriate of ammonia, and in one or two instances the carbonate of ammonia. Which is the best?"

"The one that will furnish ammonia or nitrogen at the cheapest rate,"

said the Doctor, "is the best to use. The muriate of ammonia contains the most ammonia, but the sulphate, in proportion to the ammonia, is cheaper than the muriate, and far cheaper than the carbonate."

Carbonate of ammonia contains 21 per cent of ammonia.

Sulphate of ammonia contains 25 per cent of ammonia = 21? of nitrogen.

Muriate of ammonia contains 31 per cent of ammonia = 25 of nitrogen.

Nitrate of soda contains 16? per cent of nitrogen.

Nitrate of potash, 13 per cent of nitrogen.

From these figures you can ascertain, when you know the price of each, which is the cheapest source of nitrogen.

"True," said I, "but it must be understood that these figures represent the composition of a pure article. The commercial sulphate of ammonia, and nitrate of soda, would usually contain 10 per cent of impurities.

Lawes and Gilbert, who have certainly had much experience, and doubtless get the best commercial articles, state that a mixture of equal parts sulphate and muriate of ammonia contains about 25 per cent of ammonia.

According to the figures given by the Doctor, the mixture would contain, if pure, over 28 per cent of ammonia. In other words, 90 lbs. of the pure article contains as much as 100 lbs. of the commercial article."

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 circ.u.mstances. 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 46 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 x.x.xVII.

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.

But it must be remembered that bone-dust furnishes nitrogen as well as phosphoric acid, and we are not warranted in ascribing the good effect of bones to phosphoric acid alone.

Bones differ considerably in composition. They consist essentially of gelatine and phosphate of lime. Bones from young animals, and the soft porous parts of all bones, contain more gelatine than the solid parts, or the bones from older animals. On the average, 1,000 lbs. of good commercial bone-dust contains 38 lbs. of nitrogen.

On the old dairy farms of Cheshire, where bone-dust produced such marked improvement in the quant.i.ty and quality of the pastures and meadows, it was usual to apply from 4,000 to 5,000 lbs. per acre, and often more. In other words, a dressing of bone-dust frequently contained 200 lbs. of nitrogen per acre--equal to 20 or 25 tons of barn-yard manure.

"It has been supposed," said the Doctor, "that owing to the removal of so much phosphoric acid in the cheese sold from the farm, that the dairy pastures of Cheshire had been exhausted of phosphoric acid, and that the wonderful benefits following an application of bone-dust to these pastures, was due to its supplying phosphoric acid."

"I do not doubt," said I, "the value of phosphoric acid when applied in connection with nitrogen to old pasture lands, but I contend that the experience of the Cheshire dairymen with bone-dust is no positive proof that their soils were particularly deficient in phosphoric acid. There are many instances given where the gelatine of the bones, alone, proved of great value to the gra.s.s. And I think it will be found that the Cheshire dairymen do not find as much benefit from superphosphate as they did from bone-dust. And the reason is, that the latter, in addition to the phosphoric acid, furnished a liberal dressing of nitrogen.

Furthermore, it is not true that dairying specially robs the soil of phosphoric acid. Take one of these old dairy farms in Cheshire, where a dressing of bone-dust, according to a writer in the Journal of the Royal Agricultural Society, has caused 'a miserable covering of pink gra.s.s, rushes, and a variety of other noxious weeds, to give place to the most luxuriant herbage of wild clover, trefoil, and other succulent and nutritious gra.s.ses.' It is evident from this description of the pastures before the bones were used, that it would take at least three acres to keep a cow for a year."

"I have known," says the same writer quoted above, "many a poor, honest, but half broken-hearted man raised from poverty to comparative independence, and many a sinking family saved from inevitable ruin by the help of this wonderful manure." And this writer not only spoke from observation and experience, but he showed his faith by his works, for he tells us that he had paid nearly $50,000 for this manure.

Now, on one of these poor dairy farms, where it required 3 acres to keep a cow, and where the gra.s.s was of poor quality, it is not probable that the cows produced over 250 lbs. of cheese in a year. One thousand pounds of cheese contains, on the average, about 45 lbs. of nitrogen; 2 lbs.

of potash, and 11 lbs. of phosphoric acid. From this it follows, if 250 lbs. of cheese are sold annually from three acres of pasture, less than one lb. of phosphoric acid per acre is exported from the farm in the cheese.

One ton of timothy-hay contains nearly 14 lbs. of phosphoric acid. And so a farmer who raises a ton of timothy-hay per acre, and sells it, sends off as much phosphoric acid in one year as such a Cheshire dairyman as I have alluded to did in fourteen years.

What the dairymen want, and what farmers generally want, is nitrogen _and_ phosphoric acid. Bone-dust furnishes both, and this was the reason of its wonderful effects.

It does not follow from this, that bone-dust is the cheapest and best manure we can use. It is an old and popular manure, and usually commands a good price. It sells for all it is worth. A dozen years ago, I bought ten tons of bone-dust at $18 per ton. I have offered $25 per ton since for a similar lot, but the manufacturers find a market in New York for all they can make.

Bone-dust, besides nitrogen, contains about 23 per cent of phosphoric acid.

"That does not give me," said the Deacon, "any idea of its value."

"Let us put it in another shape, then," said I. "One ton of good bone-dust contains about as much nitrogen as 8 tons of fresh stable-manure, and as much phosphoric acid as 110 tons of fresh stable-manure. But one ton of manure contains more potash than 5 tons of bone-dust."

Bone-dust, like barnyard-manure, does not immediately yield up its nitrogen and phosphoric acid to plants. The bone phosphate of lime is insoluble in water, and but very slightly soluble in water containing carbonic acid. The gelatine of the bones would soon decompose in a moist, porous, warm soil, provided it was not protected by the oil and by the hard matter of the bones. Steaming, by removing the oil, removes one of the hindrances to decomposition. Reducing the bones as fine as possible is another means of increasing their availability.

Another good method of increasing the availability of bone-dust is to mix it with barnyard-manure, and let both ferment together in a heap.

I am inclined to think this the best, simplest, and most economical method of rendering bone-dust available. The bone-dust causes the heap of manure to ferment more readily, and the fermentation of the manure softens the bones. Both the manure and the bones are improved and rendered richer and more available by the process.

Another method of increasing the availability of bone-dust is by mixing it with sulphuric acid.

The phosphate of lime in bones is insoluble in water, though rain water containing carbonic acid, and the water in soils, slowly dissolve it. By treating the bones with sulphuric acid, the phosphate of lime is decomposed and rendered soluble. Consequently, bone-dust treated with sulphuric acid will act much more rapidly than ordinary bone-dust. The sulphuric acid does not make it any _richer_ in phosphoric acid or nitrogen. It simply renders them more available.

"And yet," said the Doctor, "the use of sulphuric acid for 'dissolving'

bones, or rather phosphate of lime, introduced a new era in agriculture.

It is the grand agricultural fact of the nineteenth century."

"It is perhaps not necessary," said I, "to give any direction for treating bones with sulphuric acid. We have got beyond that. We can now buy superphosphate cheaper than we can make it from bones."