Home mixing of fertilizers is increasing in popularity. The following advantages may be mentioned: (1) The grower knows exactly the kind and amount of each ingredient used; (2) he can adapt the mixture to the needs of the different classes of crops to be grown; (3) he can adapt the mixture to the needs of the particular soil to be cropped; (4) he usually saves several dollars a ton; (5) he becomes more intelligent every year in the application of the principles relating to plant nutrition.
Numerous experiments have proved that home-mixed fertilizers are fully as valuable as factory-mixed goods of equivalent composition.
The arithmetic of home mixing is very simple. Suppose fertilizer is wanted that will contain 4 per cent of nitrogen, 8 per cent of phosphoric acid and 10 per cent of potash. (Dr. Edward B. Voorhees calls a mixture of this composition the basic fertilizer.) The nitrogen should be derived from at least two sources, say nitrate of soda, and an animal product, as dried blood. To make a more simple example, we will suppose that the nitrogen is to be derived from nitrate of soda, the phosphoric acid from rock phosphate and the potash from muriate of potash. It simplifies matters to think of percentages as pounds. Four per cent of nitrogen means four pounds in each hundred pounds or 80 pounds for the ton. As nitrate of soda contains about 16 per cent nitrogen, it is readily seen that 500 pounds of this salt will be required to furnish the required amount of nitrogen. We will suppose that the rock phosphate is 17 per cent available, and 160 pounds of phosphoric acid are needed. By dividing 160 by .17, we learn that 941 pounds of rock phosphate are required. Muriate of potash contains 50 per cent of actual potash. By calculating in the same manner it is ascertained that 400 pounds of this ingredient is required to supply the potash. These three materials aggregate 1,841 pounds. To make a ton it is necessary to add some foreign matter, as sand. The sand would be known as the filler, which is of no value, but it increases the cost of freight, drayage and application to the land.
The home mixing of fertilizers is a very simple operation. Two men provided with short-handled shovels can do the work rapidly upon any smooth floor. The bottom of the shovels should be flat and the corners square. The grower should also provide a sand screen with a 1/4-inch mesh, not less than 3 feet wide, 5 feet long, and mounted on a frame that may be propped up at any angle to the floor.
It is not convenient to mix more than half a ton at a time. The various materials are weighed and spread in a flat pile, each ingredient constituting a separate layer. The sand screen is placed conveniently near the pile and at an angle of about 45 degrees to the floor. The men stand on either side and shovel the fertilizer up on the screen. The finer particles fall through and the lumps roll to the bottom of the screen, where they can be crushed with the shovels. After the pile has been screened in this manner the screen is set aside and the pile shoveled over twice. When shoveling the bottom of the shovel should be kept on the floor to secure thorough mixing.
After mixing, the material should be rebagged in convenient amounts. A common practice is to place 100 pounds in each bag. A uniform amount in the bags is necessary to make an even distribution over the field before spreading or drilling. Mixing and rebagging should not cost more than 50 cents a ton. To prevent the forming of hard lumps the mixing should not be done more than a month before applying, especially if chemicals are largely used.