What properties does it have and what are the main components?
Alvaro Reinoso, in his book “Ensayos sobre el cultivo de la caña de azúcar”, (“Essays on sugar-cane cultivation”), first printed in Havana in1862, said the following about bat guano:
“There are, in Cuba, a great number of caves providing a considerable supply of the richest fertilizer. In these caves, where bats shelter, a fertilizer has accumulated, a true guano, the result of a mixture of solid and liquid excrement, the remains of the fruit that fed the animals, and their own carcasses. All these materials, sheltered from the sun, air and rain, form a rich mix of nitrogenous, carbonaceous and saline elements. They contain uric acid, ammonium urate, nitrates, phosphates and calcium carbonate, alkaline salts, etc. The huge quantity of guano amassed in some caves can be explained by the number of beasts that have sheltered there for so many years”.
In fact, bat guano is the most extraordinary, versatile, naturally-occurring fertilizer. It appears in a wide range of colours (white, yellow, brown, hazel, grey, black and red), a range of colour unknown in other natural fertilizers. The colour does not influence its quality, which depends on other factors, such as: the type of rock in which the guano cave formed; the feeding habits of the bat species producing the guano; the stage of mineralization in the guano, which undergoes an endless process of transformation, and the stage of maturity. So, the guano’s colour should not be associated with quality, which is determined by laboratory analysis.
This is an ecological product that has many agricultural uses, that guarantees efficient soil regeneration and abundant harvests of a high quality, making it an invaluable agricultural fertilizer for producing organic food.
This guano has a wide range of chelates (natural, organo-mineral compounds with a high molecular weight), giving it greater structural stability and an extended residual effect on the soil or the substrata on which it is applied. The freshest guano also benefits from the fauna within, whose main function is to accelerate the process of decomposition in the guano and increase its wealth of essential nutrients.
Bat guano has many excellent properties that demonstrate its value as an organic product of the highest quality, justifying the statement of many producers that it is “superior to all other natural fertilizers”.
As has been said, bat guano is found as deposits in many caves that have been inhabited by these animals, but it can also be found in smaller quantities in other places (old or abandoned buildings, trees, etc.). It consists mostly of excrement and the remains of bats that have lived in the caves for many years, and also the remains and excrement of other animals, such as mice, birds, insects, etc.
However, it is not pure animal remains and excrement in the deposits, for, over the years, these have combined with the products of rock that has been dissolved by filtering water; different chemical reactions are produced during the process that result in different characteristic substances in the guano. In caves where water filters through, soluble elements are washed out and the composition of the guano changes. Equally, the feeding habits of the bats affect its chemical composition. Another factor in guano composition is the millions of mineral particles that fall from the cave ceiling where the bats sleep. The physical and chemical action of the bats as they constantly flit about, and the release of liquid excrement at high pressure that pounds the cave walls, where thousands of bats gather, result in an invisible rain of solid mineral components, which are mixed naturally into the mass of guano deposited on the floor.
In Los Angeles, the bat guano caves are calcareous, cut out of the softer rock by the action of water over thousands of years.
This calcareous rock is composed principally of calcium carbonate with lower proportions of magnesium carbonate, sand, clay, iron oxide, aluminium oxide, sulphates, phosphates, sodium and potassium.
The clay and silica contained in the guano come from the rocks, washed out by water and deposited with other insoluble materials in the cave, where they remain unaltered.
Calcium sulphate tends to disappear, because it is slightly soluble in water, and in some cases, calcium remains only in phosphate form.
The bat excrement and remains are the main source of the elements nitrogen, phosphorus and potassium in guano. The organic compounds in the excrement contain sulphur, phosphorus and nitrogen, which form sulphuric, phosphoric and nitric acids after decomposition and oxidation. These acids react with base elements in the calcareous rock to form their corresponding salts, sulphates, phosphates and nitrates. Of these salts, all the nitrates and the sodium and potassium compounds are soluble and are washed out, while the insoluble phosphates and sulphates are deposited and accumulate in the cave deposits. These are mostly calcium, iron and aluminium phosphates and calcium sulphate.
In the fresh deposits, nitrogen is released, partly as ammonia, with its characteristically strong smell, while the rest oxidizes and forms nitrates that may be dissolved by filtering water.
Bats that feed on insects eject fragments of chitin, the main component of insects’ exoskeletons. Chitin is a nitrogenous substance that resists decomposition, which is why this form of nitrogen appears in many old guano deposits.
These distinct forms of nitrogen in the guano depend on the feeding habits of the bats living in the caves, as some colonies feed mainly off insects, while others feed off fruit.
The phosphorus contained in guano comes partly from bat excrement, but mostly from skeletal remains, although it may also come from mineral elements in the caves or remains of other animals.
Potassium, is the least represented essential macro-element, due to the solubility of its compounds, which are washed out, but some guanos have significant levels of potassium.
During the process of decomposition, the proportions of different components of the guano change – organic matter, nitrogen and potassium levels fall, while calcium phosphates, sand and clay levels rise in proportion.