FERTILIZERS 249 



prime importance as fertilizers. The inorganic substances, or mineral 

 elements of the earth, are also important but not nearly as much so as 

 the organic. The basis of all soil is mineral, and it is the decay of 

 living matter upon and within it which enriches and makes it capable 

 of producing good crops. 



The oldest forms of organic fertilizers were the remains of plants 

 that followed each other on the earth's surface. After these came 

 animal excreta. The dead bodies also of the animals themselves all 

 helped to add organic matter to the ground-up rock of which the 

 soil is composed. Material that is of organic origin is very beneficial 

 to the life of the soil. Soil is not exactly what it appears to the eye 

 to be; simply dead, inert matter. In fact, if there is any organic 

 material in it, it will be found to be teeming withhfe, from the small 

 bacterium that can only be seen under the highest powered microscope 

 to the common angle worm that supplies the fisherman's bait. This 

 life of the soil is all doing its part in changing the organic matter into 

 such shape that the plants may use it for food. This bacterial and 

 other life of the soil all require just the right amount of air, water, 

 minerals and organic matter in order that they may carry on their 

 important work. Some of the most important of these are the nitri- 

 fying organisms. These change the decaying vegetable matter into 

 such form that it can be dissolved in water and thus be taken 

 up by the plants. Some of the essential elements for plant growth 

 are calcium, iron, phosphorus, potash, magnesium, sulpher, silica and 

 nitrogen. Most soils contain enough iron, magnesia, silica and sulphur, 

 as the plants use very little of these, but nitrogen, phosphorus, potash 

 and calcium have to be constantly supplied in order to replace that 

 which has been taken out by the plants grown upon it. Heavy clay 

 soils contain more potash than the sandy soils. V 



Sources of Supply 



There are three main sources from which fertilizers can be 

 obtained : animal manures, green manures, and commercial fertilizers. 



Animal Manures 



Animal manures of all kinds are what are called complete fertili- 

 zers; this means that they supply all the essential elements of plant 

 growth; properly saved and composted so that the strawy material 

 that is used in bedding the animals is well decayed, they are as good as 

 anything which can be suppHed. Since the advent of automobiles, 

 however, stable manure is getting scarce and difficult to obtain. 



