Upon such soils as these applications of fertilizers containing phosphoric acid, and, in some cases, potash, have been found, by experience, to be most profitablea condition of affairs which could never be ascertained from the analyses. It is seldom that the increase in yield of crop bears any relationship to the quantity of the fertilizers applied. Without either fertilizers or manure, but given good tillage, yields of 300 bushels of potatoes per acre have been obtained for four successive years on the same piece of land.1

The amount of plant-food removed by any crop is small, and is obtained from all parts of the soil wherever roots extend. Most soils contain certain sufficient plantfood to supply the demands of any crop grown thereon for an indefinite period of time. To maintain crop production at a profitable point, attention must be paid to factors other than the supply of plant-food.

The ingredients applied as fertilizers will, no doubt, be found to have a value other than their value as carriers of plant-food. Their value for this purpose may be found to be small, while the benefits derived from their use may be found to be largely due to their chemical action upon the soil-e.g., as sanitary agents, promoters of the growth of desirable organisms or destroyers of injurious ones, aids in the formation of desirable chemical compounds in the soil or neutralizers of undesirable compounds, to their influence as stimulants, and upon the physical properties of the soil. That their use is desirable in some cases is evident. Why it should be, and how, are matters for investigation.

1 (N. Y.) Cornell Bul. 191, p. 192.

The farmer needs to realize that the soil on his fields to-day is not the same as that of last year. Soil is changing. The subsoil of yesterday is the soil of to-day. Although the amount removed by crops is so small that it is a negligable quantity, that removed by washing and by the wind is enormous. The muddy stream, the bars at the mouths of rivers, the movement of soils by the wind, and even the dust-cloud raised when harrowing, show that far more plant-food is removed in these ways than in crops, and to check these leaks is of more importance than to try to make up the loss by the addition of plant-food. The maintenance of a satisfactory amount of organic matter in the soil in a proper condition may usually be accomplished by a judicious rotation of crops, manuring, and liming.

"The old method has been to feed crops with commercial fertilizers, the new agriculture looks to nature for its sources of plant-food. These sources are (1) the large stores of unavailable plant-food in all soils, (2) the unlimited stores of nitrogen present in the air.'' Research has revealed the fact that soil organisms can take plant-food from both of the above sources and furnish it to growing crops, and that a fertile soil is one in which these processes are going on at the highest rate, and that it is necessary to stimulate these biological activities. Humus is a food for these organisms. Lime is essential for maintaining the soil in a slightly alkaline condition, and for fixing some of the compounds formed in the soil; and drain

1 Del. Bul. 66, p. 14.

age, deep plowing, and thorough tillage are necessary to bring air into the soil and stimulate bacterial activity. Humus, lime, and tillage are three important factors in maintaining a fertile soil,' and the farmer who understands the value of these is the one who will derive the most benefit from the use of fertilizers.

Purchasing and Applying Fertilizers. Fertilizers may be divided into three classes-viz. :

(a) Nitrogenous, or those rich in nitrogen.
(b) Phosphatic, or those rich in phosphorus.
(c) Potassic, or those rich in potassium.
Nitrogen occurs in fertilizers, as :

(1) Nitrates-e.g., nitrate of soda, nitrate of
potash.

(2) Ammonium salts-e.g., sulphate of am

monia.

(3) Organic nitrogen-e.g., dried blood, tankage,
hoof meal, etc.

Nitrogen as nitrates is immediately available

as plant-food, is soluble in water, and if
not taken up quickly by plants is liable
to be lost in the soil water; hence small
quantities applied at short intervals give the
best results.

Nitrogen as ammonium salts soon becomes

available in warm weather, and is not so
liable to be washed out of the soil as when in
the form of a nitrate.

Nitrogen as organic matter is more slowly
available.

1 Del. Bul. 66, "Soil Bacteria and Nitrogen Assimilation."

Phosphorus occurs in fertilizers, as:

(1) Insoluble phosphate of lime-e.g., floats, bone meal, tankage.

(2) Soluble phosphate of lime-e.g., acid phosphate, dissolved bone.

Insoluble phosphate of lime is considered to be but slowly available. It is converted into "soluble" by treating it with an acid, usually sulphuric acid.

The

Soluble phosphate of lime, as a rule, is more active than insoluble in promoting plant growth, but on acid soils insoluble phosphate often gives better returns. soluble phosphate of lime and a phosphate soluble in weak acids constitute the "available phosphoric acid" of the chemist. Potassium is the valuable ingredient found in : Wood ashes, kainit, sulphate of potash, double salts, and muriate of potash.

It usually gives good returns when applied to light, sandy, and peaty soils. As kainit contains chlorides and muriate of potash is a chloride, it is often advisable to apply them some time previous to planting the crop, in order that the injurious substances may be removed by the soil water, chlorides, in excess, being injurious to potatoes.

Value. All fertilizers may be valued according to the percentage of nitrogen, soluble phosphate of lime, insoluble phosphate of lime, and potash present. They are often valued on the unit system. A unit is one per

cent. of a ton, or 20 pounds; the ton, 2,000 pounds.

Unit Value.-In order to find the unit value of the different ingredients, divide the price per ton of the fertilizer by the percentage, or number, of units of the various valuable ingredients; this will give the cost per unit. For example, if sulphate of ammonia be $66.00 per ton and contains 20 per cent. of nitrogen, then 66+20=3.30 per unit (see Table, p. 45).

If the price per pound be desired, divide the price per unit by 20, or the number of pounds in the unit; thus, 3.3020 = 16.5 cents per pound.

For a fertilizer containing several ingredients, find the lowest cost of each ingredient in a standard fertilizer-as, nitrate of soda for nitrogen, muriate of potash for potash, and acid phosphate for soluble phosphoric acid and compare it with these.

Purchasing Fertilizers. In purchasing fertilizers it is advisable to write for quotations with guaranteed analyses, ascertain, as indicated above, the cheapest source of the valuable ingredients, and then purchase.

The fertilizer containing a unit of plant-food at the lowest cost is generally the one to buy. In figuring the cost always include the freight, cost of hauling, and handling; for instance, one ton of muriate of potash contains as much potash as four tons of kainit, hence the potash as muriate of potash costs only onequarter as much for haulage and handling. The same applies to high grade acid phosphate and low grade, and unless the filler is of some particular value it is wise to take the high grade or concentrated goods.

Barn Manure.-When not applied to the fields as soon as made, it should be stored under cover and the excrete from the various farm animals mixed,