marked increase in 1903, and a smaller increase in 1904, it decreased the yield of wheat in 1905, in each of duplicate tests. It is also noteworthy that the addition of potassium increased a yield of 10 bushels by 50 per cent in 1903, whereas in 1905 the maximum yield of 36 bushels per acre was

Fig. 643. Field experiments with wheat. Soil deficient in phosphorus. Plot 3 (on left) received legume catch-crops and lime; plot 4 (on right) received legume catch-crops, lime and phosphorus. See Table IV.

produced without potassium. Phosphorus produced a gain of 9 bushels in 1903, 12 bushels in 1904, and 12 bushels in 1905. (Fig. 643.)

Table V gives results secured in 1903 on the University of Illinois soil experiment field on the estate of Hiram Sibley (founder of the Sibley College of Cornell University), located on typical Illinois corn-belt soil in Ford county, Illinois. The analysis of this soil shows that the total supply of phosphorus is below that in the more highly productive soils, that the nitrogen is somewhat better supplied, while the supply of potassium is very large.

TABLE V.-CORN YIELDS FROM SOIL DEFICIENT
IN PHOSPHORUS.

four tests a decrease in yield has followed the application of potassium.

(c) Soil deficient in potassium.-In northern and north-central Illinois are extensive tracts of peaty swamp soil that is not only exceedingly rich in nitrogen and phosphorus and markedly deficient in the element potassium, as compared with normal fertile soils, but the potassium present is evidently quite unavailable under the present conditions. In places, the subsoil is of a clayey nature and when within reach of the plow it may be brought to the surface with marked benefit; but frequently the peaty material is deep or underlain with sand, and sometimes the soil only a few inches beneath the surface contains a high percentage of "alkali," including much magnesium carbonate, in which the roots of some plants, especially of corn, seem incapable of living. Table VI gives the very marked results secured in 1903 on the University of Illinois soil experiment field near Momence, Kankakee county, Illinois:

Conclusion.

In considering the general subject of culture experiments for determining fertilizer needs, emphasis must be laid on the fact that such experiments should never be accepted as the sole guide in determining future agricultural practice. If the culture experiments and the ultimate chemical analysis of the soil agree in the deficiency of any plant-food element, then the information is conclusive and final; but if these two sources of information disagree, then the culture experiments should be considered as tentative and as likely to give way with increasing knowledge and improved

Fig. 644. Field experiments with corn. Soil deficient in potassium. Plot on left received commercial potassium: plot on right received both nitrogen and phosphorus.

methods to the information based on chemical analysis, which is absolute.

Literature.

The following publications discuss in some measure culture experiments to determine fertilizer needs: Boussingault (1848), Rural Economy, (Law's Trans.); Liebig (1863), The Natural Laws of Husbandry, (Blyth's Trans.); United States Department of Agriculture, Office of Experiment Stations, Bulletin No. 22 (1895), Agricultural Investigations of Rothamsted, England (there are also many earlier reports of the Rothamsted experiments); Wagner (1891), Die Rationelle Dungung der landwirthschaftlichen Kulturpflanzen (this is only one out of many of Wagner's publications on culture experiments); New York (Cornell) Bulletin No. 129 (1897), How to Conduct Field Experiments with Fertilizers; Illinois Bulletin No. 76 (1902), Alfalfa on Illinois Soil; Illinois Bulletin No. 93 (1904), Soil Treatment for Peaty Swamp Lands; Illinois Bulletin No. 99 (1905), Soil Treatment for the Lower Illinois Glaciation; Illinois Circular No. 96 (1905), Soil Improvement for the Illinois Corn Belt.

PARAFFINED-POT METHOD FOR DETERMINING THE MANURIAL REQUIREMENTS OF SOILS.

By Frank D. Gardner

This method of determining the manurial requirements of soils consists of growing plants in small, paraffined wire pots containing soil to which have been added fertilizers of different kinds and in different quantities. The pots are planned to make possible a comparison of the several fertilizer ingredients within a period of about three weeks by means of the appearance and growth of the plants; or the effect of the treatments may be actually measured by cutting and weighing the plants, or by measuring the transpiration of the plants during the period of growth.

Description of the paraffined pot.

A special form of small pot is used. It consists essentially of soil in a wire frame surrounded by a coat of paraffin that penetrates partly into the soil, thus cementing the outer layer of soil to the vessel of paraffin. The essential feature of this is that there is no space between the soil and the pot in which the roots can develop, as is usual in other forms. In this special form of paraffined soil pot the roots are compelled to stay in the soil and tell the story of the soil, whether it be good or bad, and the relative influence of the fertilizers on it. Wheat plants are usually grown in these pots 15 to 20 days, the various fertilizer salts, organic manure or other treatment having been made on the soil previous to putting it into the pot.

This method, as outlined, is designed for both the

farmer and the practical soil investigator. It affords a ready means of determining the fertilizer or manurial requirements of a soil by getting indications in this small way, with a saving of time and labor, and the avoidance of a possible failure of returns from the use of a fertilizer to which the soil does not respond.

Fig. 645. Method of constructing the wire pot or basket.

In addition to the wire pots, the necessary apparatus includes some paraffin, an inexpensive substance that can be procured from any drugstore, and, for the weighing tests, a pair of scales that will weigh accurately to one-fourth ounce. The pots are made from galvanized-wire net having one-eighth-inch mesh, and are of simple construction (Fig. 645). The net is cut into strips 3 inches wide by 10 inches long. The ends are brought together and fastened by short rivets. At intervals along one end of the cylinder thus formed, vertical incisions one-half inch long are made, and the ends are turned in to hold the bottom, which consists of a disc of the same material. The top of the pot is then dipped into hot paraffin to the depth of about one inch, removed and dipped again, until a rim of paraffin is formed. Numbers are then attached to the pots for the purpose of identifying them, and in order that a record of each may be kept in case it is so desired. For convenience in handling, it is advisable to place the pots in shallow boxes or trays, twenty, more or less, in each. This completes the construction of the wire pot up to the time of filling it with soil.

Preparing the soil.

The soil to be tested should be representative of the field from which it is taken. A representative sample is usually secured by taking a number of small samples from different parts of the field and thoroughly mixing them. From this mixture the portions that are to be treated with fertilizers are taken, the number of portions required being one greater than the number of kinds of treatment it is desired to test.

The quantity of fertilizer added should correspond closely to the quantity used in field practice. To add these fertilizers in the proper proportions to the samples to be tested, the following procedure

is suggested: To 7 pounds of dry, well-pulverized soil add 1 ounce of the desired fertilizer. Mix very thoroughly and pass through a sieve at least twice. This mixture is still much too strong for use, and it is further diluted by adding one ounce of it to 5 pounds more of soil, mixing thoroughly as before. This new mixture contains fertilizer at the rate of 200 pounds per acre. When larger applications. are desired, proportionally larger quantities of the first mixture should be taken. For the lime treatment use only 11 ounces of soil to one of lime, instead of 7 pounds, as in the case of fertilizers. Cowpea vines and manure, being used in even greater quantity than the lime, require a still further reduction of the amount of soil in the first mixture, i. e., 4 ounces of soil to one of cowpea vines and 1 ounces of soil to one of manure. One ounce of each of these mixtures when added to 5 pounds of soil will supply lime at the rate of one ton, cowpea vines, 2 tons, and manure, 5 tons per acre.

After the fertilizers have been added to the soil, it is allowed to remain in pans or other suitable receptacles for several days, being moistened occasionally with rain-water or water from melted ice, and frequently stirred, so that the fertilizers may become thoroughly distributed. At the end of this time the soil in each pan is moistened again with water, which is ad ed until the soil is in the most favorable condition for plant growth. This varies with different soils, but with a little experience the operator can judge it rather accurately. It is important that the water used in moistening the soil be rain-water, as water from springs, wells or streams may contain mineral matter that would affect the plants, and thus vitiate the results of the tests. The soil in each pan is then divided into five nearly equal parts, and each part is placed in a wire pot, care being taken to press the soil well into the bottom and sides of the pot. The pot should be filled to within about one-half inch of the top. After filling, the soil which projects through the meshes of the wire is carefully brushed off and the pots are then ready for paraffing and planting. The pots are dipped, bottom down, into hot paraffin until an impervious layer is formed over the lower part of the pot, connecting with the rim around the top. In coating the pot, the paraffin is kept at an even temperature and the pot is dipped and quickly removed to allow the paraffin to harden, when it is dipped again, and so on until the coating has the proper thickness, about one-sixteenth of an inch.

Subsequent details of the experiment.

One or two days before the time of planting, a sufficient quantity of wheat is placed between moist cloths, covered with wet sand, and placed in a favorable place for germination. From these sprouted wheat grains those of uniform size and about the same stage of development are selected, six being planted in a row, and to the same depth in each pot. The surface of the soil is now covered to a depth of about one-fourth inch with clean, dry sand. The pots are then placed where they will be under as favorable conditions of light, temperature

and moisture as possible, care being taken to keep the pots of each set together.

The pots should be watered at frequent intervals during the growth of the plants, care being taken not to allow them to become too dry nor to make them too wet. The watering is most effectively done by means of a spray or atomizer. As a guide to the amount of water required by the pots, it is a wise precaution to weigh and record the weight of some of them when they are paraffined and planted, at which time the moisture content of the soil is favorable. By weighing these pots at intervals during the tests, the amount of water necessary to bring the soil to a favorable condition can be ascertained, and an equal amount added to all baskets that show an equal growth. At the end of fifteen or twenty days, a comparison of the growth of the plants will enable one to estimate the value of the different fertilizers. (Fig. 646.)

It should be borne in mind that this is a method not for the study of the requirements of plants, but for the study of the fertilizer requirements of

Fig. 646. Wheat plants growing in the wire baskets. No. 1, nitrate of soda; No. 2, nitrate of soda and acid phosphate; No. 3, nitrate of soda, acid phosphate and sulfate of potash; No. 4, stable manure; No. 5, untreated.

soils, in which the plant is used as an indicator. It is, therefore, not necessary to grow the plants to maturity; in fact, it would not be possible to do so successfully in the small quantity of soil used. When differences occur as a result of the fertilizer, they manifest themselves almost from the beginning of plant growth, and it is not necessary or advisable to grow the plants for periods exceeding twenty or twenty-five days from the date of planting the seed. All conditions for plant growth, except the fertilizer applications, should be equal for all treatments, so that the variations in growth may be attributed solely to the fertilizers applied. A mean temperature of about 70° F., and ranging from 50° to 90°, will prove satisfactory for wheat.

Literature.

For more detailed descriptions of this method and the results obtained with it, the reader is referred to Bulletins Nos. 23 et sequ. and Circulars Nos. 15, 16, 17 and 18 of the Bureau of Soils; Farmers' Bulletin No. 257 of the Department of Agriculture; Bulletins Nos. 167 and 168 of the Ohio Experiment Station; Bulletin No. 109 of the Rhode Island Experiment Station.

SOIL AMENDMENTS

By H. E. Stockbridge

Soil amendments are those substances, organic or inorganic, that are added to the soil for the purpose of correcting certain defects. The object of the amendment is to ameliorate the natural character of the soil so as to increase its productivity. This change or amelioration is effected by three distinct classes of action: physical, chemical, fungous and bacterial. The effects of any single amendment may involve more than one of these agencies.

Though several of the materials demanding recognition as soil amendments possess direct plantfood value, this property is outside the limits of the present consideration. It is permissible here to consider them only in their character as amendments to the soil.

Lime.

The agricultural value of lime has been recognized from a very early date. Except in its immediate relations to bacterial action, little has been added to our knowledge of its properties since the time of Thaer. Present methods of culture and fertilizing make the practical value of lime dependent almost entirely on its action as an amendment. [This subject is fully discussed in the succeeding article.]

Marl.

In many respects marl is similar in action to lime. Its active ingredient is calcium carbonate, of which it may contain over 90 per cent. The influence of marl is chiefly physical, and is due to the property of carbonate of lime of rendering light, porous, leachy soils more compact and retentive. It is a natural amendment for sandy soils, and they are often quite transformed by the physical change produced.

The marl deposits known as "green-sand" contain considerable quantities of potash and phosphoric acid that give it a recognized fertilizing value. Marls vary so greatly in composition that rules for use are suggestive only. About twice the application of lime, that would be made under similar conditions, may be suggested as a reasonable average. The material requires no preliminary treatment, other than mere drying by exposure to the air.

Chalk.

This substance is a more or less pure carbonate of lime. Its character as an amendment is essentially that of marl; indeed, many deposits of "chalk" are simply light colored marl. Such deposits are of very common occurrence in England. The Rothamsted Experiment Station is located directly over such a formation.

Gypsum, or "land-plaster."

This natural sulfate of lime has probably been used longer and more extensively as an application for increasing the productiveness of soils than

any other mineral substance. Its present use is due almost entirely to its action as a soil amendment. This action is chemical, and consists chiefly in the substitution of its calcium for the potash in different soil compounds. The potash locked up in the soil in a form unavailable to plants is thus released to enter more available combinations. Its benefits are most marked when clover or other legume is the crop following its application. The legume is able to supply its own demands for nitrogen by extraction from the air. It therefore easily satisfies its entire food requirements by the addition of the liberated potash. Its other necessities are met by most soils. It secures for itself all the nitrogen needed to go with the supply of potash liberated by the gypsum and thus makes exceptional growth.

Gypsum is a specific amendment for the "black alkali" lands of the arid West. The sterile condition of these lands, which exist in considerable areas, is due to the presence of an excess of sodium carbonate, which accumulates on the surface because of the lack of rains and percolation. Gypsum reacts on the carbonate to form the less harmful sodium sulfate and calcium carbonate. In the presence of an excess of free carbonic acid in the soil, particularly through the decomposition of large masses of vegetation, some gypsum may be converted into carbonate of lime, and exert, in a slight degree, the properties already mentioned as pertaining to this substance.

Salt.

This was originally used agriculturally under the supposition that it possessed direct fertilizing value. It possesses a solvent action on soil constituents, particularly on phosphates. This property, however, can not adequately explain the occasional marked benefits resulting from small applications of salt. Increase in the capillary movement of soil waters is sometimes the true secret of these results. Water containing small quantities of salt in solution moves through the soil more rapidly than other waters. In a given time, therefore, more water passes upward and becomes accessible to the crop. This is the real reason for the generally recognized fact that dry seasons and soils show the greatest benefit from the use of salt. Kainit.

The action of this material as an amendment is due very largely to its large content of common salt, about 40 per cent. The special advantages of its use are based on the value of the plant-food supplied-12 to 14 per cent of actual potash-and the specific action of the material as a germicide and insecticide. The price of kainit is fixed solely on the potash it contains, which as a plant-food gives full value for the investment. The salt and amending properties of the material are therefore available without cost. This is by far the cheapest way of securing salt as an amendment.

Certain unproductive soils seem to yield particularly to kainit as a corrective. Considerable areas of such land exist in the central-western states,

where they are commonly known as "bogus soils." In the Gulf states, soils of similar character are called "white-bud land." Both are low and inclined to be wet. The former tends toward peat in character, while the latter is usually more clayey. Their unproductiveness is due to imperfect drainage, and they do not yield to ordinary methods of underdrainage. The difficulty lies in the presence of a too high permanent water-table at the unproductive point, which often exists as a sterile spot in the midst of generally productive fields or sections. The Indiana Experiment Station conducted experiments for three years, resulting in a net profit of $55.60 per acre on the average crop of corn from the use of kainit at the rate of one ton per acre as an amendment on these soils. (See "Vegetation" as an amendment, below.)

Muck.

Before the use of concentrated commercial fertilizers became general, muck was one of the most common soil ameliorators. It was used under the supposition that it was an important source of plant-food, as well as an improver of the physical condition of many soils. The latter action is practically the only one justifying its present use, since actual plant-food can nearly always be secured more economically in some other form. The home use of this material, on the farms where it occurs, particularly when its direct use is as a stable absorbent, is a commendable practice. The value of muck as an amendment depends on its content of organic matter derived from partly decayed vegetation, though it usually contains onehalf to one per cent of nitrogen.

Muck absorbs about 70 per cent of its own weight of water, besides small quantities of ammonia and other gases. It greatly increases the absorptive power of friable porous soils. Its chief value, therefore, is as an amendment to sandy soils. On the other hand, it is light and porous, because of its vegetable origin, and thus improves the physical condition of tenacious clays.

The quantity of dry muck required for effecting real improvement in the character of the soils to which it is adapted is large. Forty tons per acre is not an excessive application. Its effect, however, is lasting and the total application may be gradually reached through successive seasons. Vegetation.

The growth of plants exerts material influence on soil character aside from the immediate effect on available fertility. The pulverizing action of roots, the bringing of consumed material from the lower strata to become incorporated with the surface soil, by the decomposition of the plant or its roots and leaves, are accepted facts. The plowing under of crops is one of the oldest methods of soil-improvement. Decay of vegetation results in the incorporation of much vegetable matter with the soil. This organic matter is similar to muck or peat in character and action. Organic acids are important products of this decomposition. Greenmanuring crops may thus cause a decided acid con

dition of soils, resulting in temporary unproductiveness. This result may be expected only when the decay of the green crop plowed under takes place very rapidly, under the influence of a warm humid climate. In the southern states this sour condition of the soil is almost certain to follow the turning under of such crops as cowpeas and velvet beans during the summer. The prevention lies in delaying plowing till the crop is dead and dry in the cooler autumn. Under these conditions "green-manuring" is a misnomer and is seldom really practiced. [Consult the article on greenmanures on page 503.]

Some forms of vegetable material are among the most effective applications for correcting certain recognized soil faults. The vegetable matter in animal manures exerts important influence on the physical character of soils. Coarse manure renders compact soils more porous and facilitates drainage. Decomposing manure warms cold soils and makes light soils more retentive. Vegetation possesses essentially these same properties when used without the animal intervention. Soils may be rendered either more retentive of moisture or more perfectly drained by using vegetation of corresponding physical condition. This fact has been utilized for the practical correction of an important soil defect. The conditions were mentioned in connection with the use of kainit as an amendment.

In the experiments made at the Indiana Experiment Station (see "Kainit," preceding) a layer of wheat straw three inches thick was plowed into the soil with extremely satisfactory results. In the South pine straw has been found to be equally effective. Corn, tobacco, cassava and small grains are the crops most seriously injured on these lands. Irish potatoes, on the other hand, seem to thrive fairly well without amendment.

In the experiments cited the different materials used as amendments gave the following comparative results:

It is apparent from these figures that straw closely approaches kainit, which as an amendment for these soils stands at the head of the list. On the vast number of farms where wheat, oat or pine straw is a home product, with little commercial value, it furnishes the most economical corrective for this trouble. Its use forms one of the most perfect demonstrations of the possible benefits from a purely physical amendment. The stubble of many crops, as well as all sod, possesses distinct corrective influence on soils with a tendency to excessive compactness or imperfect movement of soil waters. Wood ashes.

Though the chief agricultural value of this material lies in the plant-food contained, potash