insoluble phosphate; the importance of fineness of division was clearly shown in the discussion of tillage.

There are some soils upon which the superphosphates cannot be used without injury, usually those that are deficient in lime, the superphosphate in such cases having a tendency to make them acid. Indeed, it is even asserted that soils containing an abundance of lime in

Relative value of phosphate fertilizers. All pots received the same amounts of plant food, but 7 received its phosphoric acid from acid phosphate, 5 from bone meal and 3 from ground phosphate rock or

floats ''

the beginning may be made acid by the continued use of superphosphate if no lime is added.

When the natural phosphates alone are considered there is no doubt that the preference should be given to those derived from bones. The organic matter present in the bones decays when it is incorporated with the soil, and this process doubtless causes the phosphate to become more readily available to the plant, while the rock phosphate on the contrary is very

slowly decomposed. The degree of fineness to which bone meal or mineral phosphate is ground is of prime importance. Very fine bone meal is much more available than that which is coarser and is always rated at a higher price a ton.

Using Floats With Manure.-The use of floats, or finely ground phosphate rock, has not met with general favor, and it probably does not give good results when used alone. Some of the earlier experiments indicate that it has practically no value as a source of phosphoric acid for the plant. Recent investigations at the Ohio and Illinois Experiment Stations show that when floats is added to farm manure it has a very high fertilizing value; in fact the increased crop production in Ohio due to adding the ground rock phosphate to the stall manure was nearly as large as that obtained from the addition of superphosphate. The acid substances produced during the decay of the manure apparently make the phosphoric acid in the rock more available, and it would seem from these experiments that the comparatively inexpensive floats might, partially at least, replace superphosphate if used in connection with the manure. Other experiments have demonstrated that good results can be obtained from the use of ground rock phosphate, when plowed under with a green manure crop like clover, but that it is of very little value if used on a soil low in organic matter. In a plot experiment at the Massachusetts Experiment Station two "equal money's worth" of ground Carolina rock and superphosphate were compared. In this case the superphosphate proved superior at first, but within a few years the plot to which rock phos

phate was added gave higher yields. It would seem, on the whole, that the use of floats with manure is worthy of a trial by anyone needing a phosphate fertilizer. Ohio Bulletin 134, recommends that the ground rock be used "as an absorbent in the stable, thus securing an intimate mixture with the manure in its fresh condition."

CHAPTER XIX

MIXED FERTILIZERS

Complete Fertilizers.-Mention was made of the fact that the basic materials described in the foregoing sections contain only one, or at most two, of the essential elements of fertility. By far the larger part of the commercial fertilizers used by the farmers in this country are purchased in the form known as complete fertilizers. A complete fertilizer, in the sense in which the word is used in trade, is one that contains nitrogen, phosphoric acid and potash, in proportions that are supposed to be suited to the requirements of farm practice. Practically all of these fertilizers are made by mixing two or more of the basic materials heretofore described, the different ingredients being so combined as to give the desired percentage of nitrogen, phosphoric acid and potash. In case the basic materials alone yield a product that is richer in the essential ingredients than is desired by the manufacturer, sufficient gypsum, dry earth, peat or other inert matter is added to bring the percentage of these ingredients down to the desired point. Materials added in this way are known as fillers. These fertilizers are indiscrim

* There is a mistaken notion which is quite prevalent that anything contained in a fertilizer except nitrogen, phosphoric acid and potash is a filler. As a matter of fact it is impossible to make any rational combination of the basic materials which will contain more than one-third of its total weight of the three "essential ingredients," for even in the

inately recommended for general use and all sorts of startling claims are made for them by the various manufacturers. They are offered as universal fertilizers, irrespective of the well known fact that soils differ widely in their characteristics and that the crops vary in their food requirements. To be sure, a fertilizer of this kind if sufficiently rich in nitrogen, phosphoric acid and potash might be made to produce a large yield on any kind of soil if used in quantities, but such a use of a fertilizer would result in adding some of the elements at least in amounts far in excess of the need of the crop. The profits of ordinary farming are not sufficient to warrant the application of any of the elements of plant food in larger quantities than is required by the plant. An economical use demands that fertilizers be adapted to the soil, and to the crop to be raised, and this end can rarely be attained by the use of complete fertilizers. A little thought on the part of the farmer will convince him that the use of these general fertilizers is irrational, and that to obtain the best results he must adopt some system of fertilization especially adapted to his particular conditions.

Special Fertilizers.-A large number of so-called special fertilizers now offered by the manufacturers are supposed to be adapted to the particular needs of a special crop or class of crops. Each fertilizer usually bears the name of the particular crop for which it is designed. Such fertilizers are offered for all of the

highest grade materials the nitrogen, phosphoric acid and potash are combined with other substances. A filler, properly speaking, is a substance added for the express purpose of diluting the fertilizer and usually contains no plant food whatever. No filler is used in the highest grade mixed goods.