Fish contain a high percentage of nitrogen and phosphoric acid, and consequently when fish are digested and the carbon is burnt out of them, the manure that is left contains a still higher percentage of nitrogen and phosphoric acid than the fish from which it was derived.
Guano is digested fish. If the guano, or the manure from the birds living on fish, has been preserved without loss, it would contain not only a far higher percentage of nitrogen, but the nitrogen would be in a much more available condition, and consequently be more valuable than the fish from which the guano is made.
The difference in the value of guano is largely due to a difference in the climate and locality in which it is deposited by the birds. In a rainless and hot climate, where the bird-droppings would dry rapidly, little or no putrefaction or fermentation would take place, and there would be no loss of nitrogen from the formation and escape of ammonia.
In a damper climate, or where there was more or less rain, the bird-droppings would putrefy, and the ammonia would be liable to evaporate, or to be leached out by the rain.
Thirty years ago I saw a quantity of Peruvian guano that contained more than 18 per cent of nitrogen. It was remarkably light colored. You know that the white part of hen-droppings consists principally of uric acid, which contains about 33 per cent of nitrogen.
For many years it was not difficult to find guano containing 13 per cent of nitrogen, and genuine Peruvian guano was the cheapest and best source of available nitrogen. But latterly, not only has the price been advanced, but the quality of the guano has deteriorated. It has contained less nitrogen and more phosphoric acid. See the Chapter on “Value of Fertilizers,” Page 324.
SALTS OF AMMONIA AND NITRATE OF SODA.
“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 quantity 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 grass or clover-seed.”
“The best plan,” said the Doctor, “is to mix them with sifted coal-ashes, or with gypsum, or sifted earth.”