119. Rotations.-The rotation of crops has been shown to be absolutely essential to the profitable use of commercial fertilizers.1 Rotations are greatly modified in different localities both by the crop producing capacity of the soil and by economic causes. Wheat is frequently grown because it cannot well be omitted from certain otherwise successful rotations. In many sections for seeding land to timothy and clover, no other crop combines so many advantages.

The five course rotation of maize, oats and wheat, each one year, and timothy and clover two years, is considered standard in many sections. In this rotation stable or farm yard manure is applied to the land before plowing for maize at the rate of about twenty loads per acre. On what is known as maize land, the residual effect of this manuring is usually sufficient to grow a good crop of wheat, provided other conditions, such as climate, rainfall and insect enemies, are not unfavorable. On the more tenacious light colored clay soils, a light application (say twentyfive pounds) of phosphoric acid (PO) is applied at the time of seeding the wheat. A slight modification of the above is the four course rotation of maize, oats, wheat and clover, each one year. A still further modification is the three course rotation of maize, wheat and clover, each one year. This is in regions not well adapted to oats on account of climatic conditions and on soil in which wheat can be successfully raised after maize without plowing. (128) Sometimes mammoth clover is used and treated as a seed crop. One of the most satisfactory rotations in its effect upon the yield of wheat is the three course rotation of potatoes, wheat and clover, each one year. Where stable or farm yard manure is available it is applied to the clover immediately after cutting the second crop in order to stimulate the growth of clover to be plowed under either in the late fall or early spring. In many cases the land is quite heavily fertilized with commercial fertilizers at the time the potatoes are planted.

1 Ohio Bul. 110 (1899), p. 68.

The wheat is sown after the removal of the potatoes without plowing. The residual effect of the fertilizers combined with the influence of the tillage given the potatoes usually results in increased wheat production.

120. Carriers of Fertilizing Constituents. The results of many experiments with various forms of phosphatic fertilizers seem to indicate clearly that when these are applied to wheat, the carrier or source of the phosphoric acid, whether raw bone meal, undissolved rock phosphate, basic slag, acid phosphate, or tankage, does not materially affect the yield provided the material is finely ground. Nitrate of soda has been found to be the most effective carrier of nitrogen, although the difference in the effectiveness of different carriers of nitrogen is not great when applied to wheat.

121.

Relative Importance of Fertilizing Constituents.-While field experiments indicate that the relative importance of fertilizing constituents depends upon the soil, throughout the drift area of the United States, phosphoric acid is the only fertilizing ingredient which, when applied singly, has been found generally to increase the yield of wheat. The increase in the yield of straw has usually been greater than the increase in grain. (53) For this reason, the increased appearance of the crop is generally greater than the increased yield of grain. The influence of fertilizers upon the seeding of timothy and clover when it accompanies the seeding of the wheat is often decidedly favorable. Neither nitrogen nor potash when used alone produces generally any marked influence on the yield, but both, and nitrogen especially when applied with phosphoric acid in proper proportions, appear to exert a favorable influence. The Ohio Station has found that a complete fertilizer, containing all three constituents, has produced a much larger total increase than the sum of the increase produced by the constituents used separately. The same idea is expressed in the results obtained 1 Ohio Bul. 110 (1899), p. 68.

in a five year rotation of maize, oats, wheat, each one year, and clover and timothy two years, fertilizer being applied to each of the grain crops:

"When phosphoric acid has been applied alone in superphosphate, 20 per cent of the quantity applied in the fertilizer has been recovered in the crop. When phosphoric acid has been reinforced with potash, there has been a recovery of 27 per cent of the former. When phosphoric acid has been reinforced with nitrogen instead of potash the recovery has reached 38 per cent of the phosphoric acid applied, and when both potash and nitrogen have been added, the recovery of the phosphoric acid has amounted to 46 to 50 per cent."1

Wheat does not appear to be benefited directly by the application of lime. If the soil needs liming, it is best applied to the land prior to planting it to maize.

122. Amount of Fertilizers.-A standard application of fertilizer may be said to be one that furnishes from ten to twenty pounds each of ammonia and potash and from thirty to sixty pounds of phosphoric acid. This can be obtained by applying from 250 to 500 pounds of a commercial fertilizer containing four per cent of ammonia, twelve per cent of available phosphoric acid, and four per cent of potash. This is often referred to as a 4-12-4 fertilizer and is a grade that usually can be found on the market.

The ratio of phosphoric acid to nitrogen and potash should be varied somewhat with state of fertility. With soil quite exhausted through continuous culture the proportion of nitrogen and potash to phosphoric acid should be increased, while with land of higher fertility and with favorable rotation, nitrogen and potash may be reduced. The above figures are at best only general averages.

When it is necessary to apply lime to wheat land, an amount equal to 1,000 to 1,500 pounds of quick or freshly burned lime (CaO) may be applied. When it is water-slaked it will have increased in weight thirty-two per cent (CaO: Ca(HO),::100:132).

1 Ohio Bul. 110 (1899), p. 57.

123. Time and Manner of Applying Commercial Fertilizers.Commercial fertilizers are applied to wheat lands by sowing broadcast just in front of the wheat drill or by applying at the same time the wheat is drilled by a fertilizer attachment. The latter method is much to be preferred. In some cases an additional application of nitrogen is made to winter wheat by sowing nitrate of soda broadcast in the spring. At the experiment stations it has been customary to apply onefourth of the nitrogen in the fall, often in the form of dried blood, and the rest of the nitrogen in the spring in the form of nitrate of soda, on the theory that if all the nitrogen is applied in the fall in a soluble form, much of it would be lost through drainage during the winter. Where nitrogen is applied in the spring, care should be taken to apply it before the wheat plant has made much growth. (113)

In case lime is used, it should be spread upon the plowed land three or four days before seeding, immediately harrowed in and allowed to remain until all lumps which may be present have slaked, when the ground should be stirred again, preferably with a spring tooth harrow.

124.

Farm Manure.-Farm manure is usually applied to some other crop in the rotation, as maize, rather than directly to the wheat. If applied directly to wheat land, better results will be obtained by applying 200 tons to twenty acres of wheat than by applying the same amount to ten acres. If the preceding crop has been oats, the manure should be spread as soon as possible after the oats are cut and the land plowed. It is desirable that the manure should be well rotted, where rainfall is liable to be deficient. Beginning with a virgin soil, the Central Experiment Farm has found, however, after sixteen years that fresh and well-rotted manure applied in equa! weights gave equal yields of grain and straw, while barnyard manure gave considerably higher yields than any form of commercial fertilizers, and about twice the yield of plots not

fertilized.1 Farm manure may be applied to the land after the wheat is sown, if well rotted, preferably with a manure spreader, if the condition of the land is such as not to be cut up too much with the spreader. Experiments have shown that a ton of stall manure will produce a larger return of wheat than a ton of yard manure.2

Farm manure does not produce as large returns for the fertilizing constituents contained as commercial fertilizers when applied to wheat; nevertheless its lower cost often makes its use profitable. Where there is a limited quantity of farm manure or where both farm manure and commercial fertilizers are used, the best practice usually is to apply the farm manure to land for maize and apply the commercial fertilizers, if deemed desirable, to the land for wheat.

3

125. Mulching.-Mulching wheat with straw or other material for the purpose of winter protection has not been generally practiced. The Ohio Station has tested the value of mulching for a series of years, and has found no practical benefit from the use of a mulch. In severe seasons the benefit has been very slight, while in mild seasons the mulch has usually been harmful. A heavy mulch was more harmful than a light one. The Tennessee Station obtained about five per cent less yield from a lightly mulched plat than from one which was not mulched.

In exposed situations and localities where there is little snow upon the ground, a light mulch may be beneficial to the wheat. But where there is considerable snow and the temperature more uniform the mulch is pretty certain to do more injury than good. Mulching, however, must not be confused with a top dressing of stable manure for the purpose of adding fertility to the soil.

1 Can. Expt. Farms Rpt. 1903, p. 24.

2 Ohio Bul. 110 (1899), p. 52.

8 Ohio Bul. 82.

4 Tenn. Vol. III, Bul. 2.