This section is from the book "A Dictionary Of Modern Gardening", by George William Johnson, David Landreth. Also available from Amazon: The Winter Harvest Handbook: Year Round Vegetable Production Using Deep Organic Techniques and Unheated Greenhouses.
This now celebrated manure has been known as the chief fertilizer employed by the Peruvians, almost as long as that part of the New World has been recognized by geographers. Its name, in the language of that country, signifies the manure-and it merits such distinction, as being one of the most powerful assistants to vegetation which can be applied to the soil. Guano is not peculiar to Peru, but is found in immense beds upon many rocks and islands of the Atlantic, being the excrements of the marine birds frequenting those ocean solitudes. It has been lately analyzed by Dr. Ure, who reports it as composed of the following proportional constituents:-
Azotized organic matter, including urate of ammonia, and capable of affording from 8 to 17 per cent, of ammonia by slow decomposition in the soil . . .
Phosphate of lime . .
Ammonia, phosphate of"" magnesia, phosphate of ammonia, and oxalate of ammonia, containing from 4 to 9 per cent, of ammonia
Siliceous matter . . .
This analysis explains the source from whence failure has been derived to many who have tried it. It is the most violently stimulating of all the known natural manures, and they have applied it too abundantly. This is shown by the experiments of Mr. Maund. When applied to Strawberries once a week in a liquid state, (four ounces to a gallon,) it made them very vigorous and productive; but sprinkled upon some young seedlings of the same fruit it killed them. Two ounces per yard, (five cwt. per acre,) were sprinkled over Onions, and they doubled the untreated in size. Potatoes manured with one ounce and a half per yard, were rendered much more luxuriant than others having no guano. Brussels Sprouts were half destroyed by being planted in immediate contact with nine parts earth and one part guano. Geraniums were greatly injured by liquid manure of guano, (four ounces per gallon,) but "Plants of various sorts in pots, watered only with guano water, half an ounce to a gallon, have flourished astonishingly; none have failed.
These are lessons which cannot be mistaken." - Auctorium, 223. Mr. Rendle and other persons record, as the result of dearly-purchased experience, that where guano has failed to be beneficial, or has been injurious, it has been applied in quantities too powerful for the plants to bear. In a liquid state, half an ounce per gallon, and given to growing plants once a week, it never fails to be productive of vigour.
There is reason to fear that all the. advantages attributed to Guano, may not be realized. That it has produced striking effects on certain crops cannot be questioned - especially on grass, wheat and Indian corn; but we are far from subscribing to the opinion of those who in their zealous praise of this new fertilizer, assert that it is cheaper to buy it, than haul manure from the barn-yard to the fields!
There are many crops on which it appears to produce but little effect:! The writer has used over two tons of what was reputed to be the best Peruvian guano, in experiments, chiefly on Kitchen garden vegetables carefully noting the quantity applied, mode, etc, but in nearly every instance without perceiving any important result. - Doubtless much depends on the soil, and the presence or absence of those constituents which abound in guano - where they already exist in the soil, in sufficient quantity, no benefit can result from its application.