COMMERCIAL FERTILIZERS 57 



little phosphoric acid. (2) Crushed tankage, containing 4 to 

 9 per cent, of nitrogen and 3 to 12 per cent, of phosphoric 

 acid. There is a kind of tankage called digester tankage which 

 can be used for feeding animals as well as for fertilizer. 

 When buying it one should state for which purpose it is to 

 be used, because that for fertilizer purposes only may contain 

 chemicals that would be injurious to animals. Tankage also 

 decays rather quickly. 3. Dried ground fish or fish guano, is 

 made from a kind of fish called menhaden, caught along the 

 Atlantic coast. The fish are steamed and pressed to get out 

 the oil. The pomace is then ground and made into fertilizer 

 which contains about 6 to 8 per cent, each of nitrogen and 

 phosphoric acid. Some of the fish fertilizer comes from the 

 wastes of fish markets and fish canneries. The nitrogen and 

 phosphoric acid in these is quite variable. Fish fertilizq^'s 

 give up their plant food about as easily as tankage and dried 

 blood. 4. Cottonseed-meal is usually used as a cattle food, 

 but it can be used as a fertilizer as well. It is made from 

 cotton seeds. The covering of the kernel is first taken off, 

 then the kernel is ground and pressed to get out the oil. The 

 pomace is called cottonseed-meal. It contains 6 to 7 per cent, 

 of nitrogen and 1 to 2 per cent, of phosphoric acid. It makes a 

 good fertilizer and is quickly available. When we say that 

 a fertilizer is quickly available, we mean that it soon decays 

 in the. ground and gives up its plant food to the roots of 

 plants. 5. Guanos are composed mainly of the excrements 

 of fish-eating birds. W^here large numbers of sea birds roost 

 on the islands in rainless regions their droppings soon accu- 

 mulate in large quantities. These are collected and shipped 

 to farming regions. Most of the guano comes from islands 

 lying off the coast of Peru, and is called Peruvian guano. 



