the richest in nitrogen of all fertilizing materials, containing from 20 to 23 per cent. At the present time the high price of sulphate interferes with its extensive use as a fertilizer, although it gives excellent results on soils that contain plenty of lime.. It should never be used on soils deficient in lime nor in connection with the ordinary potash fertilizers which contain chlorine.

Nitrate of Soda or Chili Saltpeter is a crystalline substance somewhat resembling coarse salt in appearance and is entirely soluble in water. It all comes from large deposits in Chili which supply over one million tons of nitrate a year to be used as a fertilizer. Chili saltpeter contains from 15 to 16 per cent of nitrogen in a form that is immedaitely available to the plant, and for this reason it is the most desirable nitrogenous fertilizer to use where immediate results are desired. It is not fixed by the soil and consequently should be supplied only as the crop can use it, and never applied to the ground when it is bare. As it is so easily washed from the soil it is considered best to use it in two or three applications instead of applying all at one time.

Relative Availability of Nitrogenous Fertilizers.The percentage of nitrogen present in the different fertilizing materials as given in the previous section does not properly indicate their relative fertilizing value. Mention has repeatedly been made of the fact that the plant can make use of the nitrogen only when it is present in the soil in the form of nitrates. Nitrate of soda is the only fertilizer on the list that contains nitrogen in the nitrate condition, and consequently is the only one that adds nitrogen to the soil in a form that is

available to the plant without further change. All the other materials must undergo the process of nitrification, and have their nitrogen converted into nitrates before they can be used by the crop. It must be apparent, then, that the value of a nitrogenous fertilizer depends both upon its content of nitrogen, and the ease with which it is nitrified.

Of the list given above, sulphate of ammonia is the most easily converted into nitrates provided the soil is abundantly supplied with lime. Next in order comes dried blood. So many other uses are being discovered for dried blood, however, that the time is probably not far distant when it can no longer be used as a fertilizer.

The nitrogen in dried fish, tankage, hoof meal and bone meal are readily changed by nitrification and rank next to blood meal. Horn meal, on the other hand, decomposes very slowly, and the nitrification of leather is so slow as to make it practically worthless as a fertilizer.

Experiments up to date indicate that if nitrate of soda is rated at 100 per cent, the availibility of the other materials would be as follows:

"If for example the increased yield of oats due to the application of nitrate of soda is 1,000 pounds, the

yield from blood would be 700 pounds, from hoof meal 650 pounds and from leather 20 to 300 pounds."

These statements indicate how little an analysis of a fertilizer which gives only the per cent of nitrogen or ammonia tells of the real value as a supplier of nitrogen, and show very clearly that to arrive at any conclusion regarding the value of a nitrogenous fertilizer one should know the source or condition of the nitrogen as well as the per cent.

Two or three suggestions for the selection of nitro

Effect of top dressing grass land with nitrate of soda. The plot on the left received no nitrate, the center one half ration, and the one on the right a full ration of nitrate.

gen fertilizers may be deduced from this discussion. For those crops which begin their growth early in the spring the best results will follow the use of Chili saltpeter, as the soil is likely to be poor in nitrates and the process of nitrification slow at that time. Such crops as have very short periods of growth will respond best to nitrogen in nitrates. Corn, on the other hand, and the other crops which make their growth after the season is well advanced can use the slower acting fertilizers, as can also those crops which occupy the ground permanently. Some agriculturalists prefer to use a fertilizer containing nitrogen in three forms

for the crops that grow during the greater part of the season, a little nitrate of soda for immediate use, sulphate of ammonia to supply nitrogen a little later and tankage to carry the plant to maturity, all these materials being mixed and applied at one time.

Nitrogen is Expensive.-Nitrogen is the most expensive element to supply in commercial fertilizers, costing as it does at least three times as much a pound as either phosphoric acid or potash. In ordinary or "extensive" farming it is seldom profitable to use nitrogenous fertilizers for the nitrogen of the soil can be readily maintained by means of the farm manure, and a proper use of leguminous crops in the rotation. Market gardening and other forms of intensive farming call for a liberal use of fertilizers containing nitrogen. A careful study of the materials used to supply nitrogen should be made by those engaged in this style of farming for as Wagner says, "The art of manuring is dependent upon a rational application of nitrogen."

CHAPTER XVIII

POTASH AND PHOSPHATE FERTILIZERS

Potash Sometimes Necessary in a Fertilizer.—It has been shown that most soils contain much more potash than nitrogen or phosphoric acid. The greater part of the potash in the soil is in very insoluble and unavailable forms, and although there are large quantities present the plant may be able to use so little of it that a good crop is impossible, as has been shown by the increased yield from the use of potash on clay soils that had a high content of this element of fertility. "It has been attested that potash is of relatively less importance than either nitrogen or phosphoric acid, inasmuch as good soils are naturally richer in this element, and because a less amount is removed in general farming than of either nitrogen or phosphoric acid, as the potash is located to a less extent in the grain than in the straw, which is retained on the farm. It is, however, a very necessary constituent of fertilizers, being absolutely essential for those intended for light, sandy soils and for peaty meadow lands, as well as for certain potash-consuming crops, as potatoes, tobacco and roots, since these soils are very deficient in this element, and the plants mentioned require it in larger proportion than do others. In fact it is believed. by many careful observers,-and the belief has been substantiated in large part by experiments already con