Chapter 38

THE USE OF STABLE MANURE

Controlling Factors.--The farm supply of stable manure is a carrier of plant-food, returning to the soil four fifths of all the fertility removed in the crops fed, but it is much more than this. Land which receives only plant-food, as may be the case when fertility is supplied in commercial fertilizers, loses good physical condition. Organic matter is needed for maintenance of physical condition, the retention of soil moisture, the freeing of inert minerals in the land, and the promotion of bacterial life in the soil. No small share of the value of a ton of manure is due to its organic matter. This is a factor in the problem when deciding what disposition of the manure will pay best. One field may be in condition to respond fully to the use of commercial fertilizers, while another is too deficient in humus for best results. Some crops are more insistent upon supplies of organic matter than others.

Again, the disposition of the manure depends upon the supply. If most crops are fed on the farm, the manure is a leading source of fertility for all fields and crops, and may be used once or twice in the crop-rotation on every field. If the manure is in small amount, due to a scheme of farming involving the growing of crops for market, the function of the manure may be only to encourage the starting of sods, in which legumes are a leading factor.

Direct Use for Corn.--The practice of spreading manure on grass land for corn is based upon much good experience. The custom is nearly universal in regions where corn is an important part of a four, five, or six years' rotation, and all of the corn and hay is fed on the farm. This disposition of the manure permits the handling at times when other work does not rush. The supply carried over from the spring is put on in late summer, and the manure made in the early part of the winter can be drawn to the field fast as made. Manure spread immediately before the sod is broken is less effective, as no leaching of soluble elements into the surface soil occurs before the coarse material is buried in the bottom of the furrow.

The use of fresh manures for corn is rational, because corn is a gross feeder and requires much nitrogen. All plants having heavy foliage can use nitrogen in large amounts. It is possible to apply manure in excessive amount for this cereal, the growth of stalk becoming out of proportion to the ear, but the instances are relatively few. Ordinarily corn suffers from lack of nitrogen. When the farm manure is in large amount, its direct use for corn is good practice.

Effect upon Moisture.--Coarse manures should not be plowed down late in the spring, as they increase the ill effects of drouth. Decayed vegetation, well mixed with the soil, increases the soil's water-holding capacity, but undecayed material in the bottom of the furrow is harmful. Fresh, strawy manure, made immediately before the time for breaking a sod, is preferably carried over in a covered shed until a later season of the year.

When manure has been spread upon a sod in the fall or early winter, it decays quickly after the plowing, and aids in resistance to drouth. When it is plowed down, the ground is kept more porous, and the presence of plant-food and moisture at or near the depth of plowing encourages deeper rooting of plants, and thus indirectly assists them to withstand dry weather. If the plowing is good in character, leaving the furrow-slice partly on edge, and permitting the harrow to mix part of the turf and the manure with the remainder of the soil, the best conditions respecting moisture are secured.

Manure on Grass.--When the crop-rotation embraces two or more years of grass, or one of clover followed by only one of grass, it is better practice to use the manure to thicken the sod. The object in view is the largest possible amount of crops, and the maximum amount of organic matter for the soil. Grass is a heavy feeder, like corn, and makes good use of nitrogen. Its roots fill the soil so that no loss attends the use of manure. When the supply is given the grass, after the harvest of the second crop of clover and during the winter, the timothy can make a rank growth. The part of the plant above ground has corresponding development below ground. Not only does a large increase in the hay crop result, but the heavy mass of grass roots, the aftermath, and the remains of the manure provide a great amount of fertility for the corn which follows. The increase in hay permits a corresponding increase in the manure supply the next year, if it is fed, and if it is sold on account of a market price greater than its value for feed and manure, it adds to income materially--and that is one reason for farming.

Manure on Potatoes.--There are excellent cash crops that may get more than their fair share of the farm supply of fertility, and against the interest of fields in the farm not adapted to cash crops. The justification is found in the farm ledger. In some regions potatoes are the best crop in point of net income per acre, where the acreage is kept restricted so that there may be plenty of organic matter to help in conserving moisture. It is not good practice to use fresh manure, and especially that from horse-stables, for potatoes. A heavy application makes an excessive growth of vine, and the yield of tubers suffers. A stronger deterrent is the effect that fresh manure has on the development of the spores that produce the disease known as potato-scab. Rotted manure is less dangerous, and few crops repay its use in higher degree than the potato. Some growers prefer to make heavy application of fresh manure to grass for corn, and follow with potatoes so that they can profit by the rotted organic matter that remains. In this way the physical condition is made excellent, moisture is well held in a dry season, and commercial fertilizers can supplement the plant-food left in the manure.

When to plow Down.--Excellent farmers differ regarding the relative efficiencies of manure plowed down and that mixed with the top soil. Both classes may be right for their individual instances. The plowing down of manure helps to deepen the soil, and that always is desirable. It causes plants to root deeply, and that is a distinct benefit in a drouthy season, and always desirable. When a soil is in such tilth that the breaking-plow always brings fertile soil to the surface, the plowing down of manure gives excellent results, though it should be permitted to leach at the surface for a few weeks before being turned under. When land is being prepared for a seeding to grass or clover, the supply of manure should not be plowed down wherever the breaking-plow brings soil to the surface that is deficient in humus. In the latter case the manure always should be used as a top-dressing, and should be evenly spread and well mixed with the surface soil. It is needed there far more than it can be needed farther down. The surface soil always should have a high content of organic matter.

Heavy Applications.--When the farm supply of manure is small, applications should be light. The manure should not be the dependence for plant-food on a part of a field, or a single field of the farm, under such circumstances. It is more profitable to give a light dressing to a larger area. The manure is needed to make a fertilizing crop grow, and a very few tons per acre can assist greatly, when rightly used. The manure is needed to furnish bacteria to the soil, and a small amount per acre is useful for this purpose. Always there is temptation to use all the manure on a field convenient to the barn, and to concentrate it on a sufficiently small area to make a good yield sure. The loss to the farm in this method is heavy. The thin spots and the thin fields have first right to the manure as a top-dressing, and six tons per acre will bring larger returns per ton than twelve tons per acre. At the Pennsylvania experiment station the land receiving ten tons of manure per acre in the common four years' rotation of corn, oats, wheat, and mixed clover and grass gives added returns of $1.63 a ton, while an application of eight tons pays $1.85 a ton, and a six-ton application brings the value per ton up to $2.41. These applications are made twice in the four years.

Reënforcement with Minerals.--A ton of mixed manure in the stable contains about ten pounds of nitrogen, five pounds of phosphoric acid, and ten pounds of potash. This makes the percentage of nitrogen and potash the same, while the percentage of phosphoric acid is only half as high. A commercial fertilizer of such percentages would be esteemed a badly balanced one. Certainly the phosphoric acid should be relatively high, as this constituent of plant-food runs low in the soil. If 50 pounds of 14 per cent acid phosphate were added to each ton of manure while it is being made in the stable, seven pounds of phosphoric acid would be added, making the percentage in the manure a little higher than that of the nitrogen and the potash. A better balance is given to the fertility. There cannot be any loss in this purchased plant-food, if the stable floor is tight. Fermentation cannot drive it off, and when applied to the soil it is tightly held. Practically no phosphoric acid is found in drainage waters. Eight tons of manure thus reënforced would contain the same amount of plant-food as a ton of fertilizer having 4 per cent nitrogen, 5 per cent phosphoric acid, and 4 per cent potash. The addition of the 50 pounds of acid phosphate per ton does not bring the phosphoric acid content up as high relatively as in most commercial fertilizers, but it helps. The total amount in the eight tons manure may be sufficient, and the greater part of the total has sufficiently immediate availability, while the manure must undergo decomposition, and some of the nitrogen and potash does not become available within the year.

Durability of Manure.--Tests of the durability of manure in the soil involve some uncertain factors, but we are interested only in the effects of applications. These effects may continue for a long term of years, and an example will illustrate. Land may be too infertile to make a good clover sod. If a good dressing of manure be given half the land, affording proper conditions for making a sod, the result will be a heavy growth of clover, while the seeding on the unmanured half will be nearly a failure. If no manure or fertilizer be used in the crop-rotation, the probability is the manured portion of the field will again make a fairly good sod. How much this success may be due to the remains of the manure, and how much is attributable to the effect of the clover and to better bacterial life introduced and favored by the manure, no one knows. Probably the greater part of the benefit comes only indirectly from the manure applied three or four years previously. Half of the field may thus be lifted out of a helpless state and remain out of it for a long term of years, while the other half grows only poorer. A probable illustration of this lasting indirect effect may be seen in one of the plats in the soil fertility experiments on the Pennsylvania experiment station farm.

Experiments at the Rothamstead station, England, show some lasting results from applications of manure. Director Hall cites the case of one plat of grass land which was highly manured each year from 1856 to 1863, and has since been left unmanured. In 1864 this plat gave double the yield of an adjoining plat which had been left unmanured during the eight years. In 1865 the plat, last manured in 1863, gave over double the yield of the unmanured. In the following ten years its yield was a half more than that of the unmanured. In the next ten years the yield was a quarter more. In the next ten years it fell to 6 per cent more than the plat that had received no manure in the beginning of the experiment. In the following ten years it rose to 15 per cent. Here is a lasting effect of manure for over forty years where grass was grown continuously.