Farm Manure

Myron S. Anderson.

This chapter is based on a chapter by Robert M. Salter and C. J. Schollenberger in the 1938 Yearbook of Agriculture.

Livestock on American farms each year produce a billion tons of manure. It has great potential value, and its organic matter is twice the amount of humus that the soil gets from our grain and cotton crops.

Manure has value in maintaining and improving soil because of the plant nutrients, humus, and the organic substances it may contain.

About 250 thousand tons of dried animal manures, bagged and in bulk, are sold each year in the United States. Four-fifths of it is produced and sold in Pacific Coast States. Near Los Angeles alone, about 5 million bags of manure, with a retail value of 3.5 million dollars, are used annually.

Much of the manure sold in the West is produced by dairy cattle on ranches and farms where little or no feed is grown.

Gardeners in the East apply considerable amounts of dried manures, which originate in commercial dairies and in stockyards. The manures, dried and bagged, often are sold with a guaranteed nitrogen content of 2 percent. Superphosphate is sometimes added before the manures are dried. Such products may have a guaranteed content of phosphoric oxide.

The values of manure on irrigated and on nonirrigated lands vary with the market prices of crops and have been estimated within the range of 2 dollars to 6 dollars a ton when field crops are grown.

If we assume an average value of 2.50 dollars and the recovery of two-thirds of the potential manure production from feeding all crops except wheat grain, the annual value of the manure from 100 acres of land that produces 50 bushels of corn, 40 bushels of oats, 25 bushels of wheat, and 2 tons of hay an acre in rotation would be about 500 dollars.

But only about one-third or one-half of the potential crop-producing and soil-conserving value of the manure actually is utilized. Probably one-half of it is dropped on pastures and uncultivated ground. Of the rest, an enormous loss occurs because of failure to save the liquid portion; improper fermentation and drying, whereby nitrogen is lost; and leaching from storage piles exposed to heavy rainfall.

Even after it is spread on the field, the manure may lose a great deal of ammonia through volatilization before it is incorporated into the soil, and a part of the soluble constituents may be lost in surface runoff.

A final factor in the inefficient use of manure is that it is not always applied at the season, in the manner, at the rate, or to the crop that would give the greatest return.

It is possible to prevent much of this loss if one understands the nature of manure, the character of its most valuable constituents, and how it may be utilized best.

The maximum benefits can be realized by handling and storing the manure properly; using it on suitable soils; applying it at the proper place in a rotation as regards crop or crops; using supplemental fertilization and lime, if needed; installing adequate drainage and irrigation, if needed; using high-quality, well-adapted seed; and observing good tillage practices.

FARM MANURE is a mixture of animal excrements and the soiled bedding that accumulates in stables.

Average farm manure in a damp condition is usually assigned the formula of 0.5-0.25-0.5 meaning, respectively, the percentages of nitrogen phosphoric oxide, and potash.

At least two-thirds of the nitrogen is in slow-acting forms. Commercial fertilizer equivalent to 1 ton of average manure could be bought at retail for about 2.50 dollars in 1957. The expense of applying 100 pounds of 10-5-10 fertilizer is much less than that of applying a ton of manure. On soils in good tilth, the returns from an equivalent amount of fertilizer usually will be greater. Many persons therefore discount the value of manure as fertilizer.

Experiments in Denmark in 1894-1948 compared crop yields from plots treated with farmyard manure and plots treated with equal amounts of plant nutrients as artificial fertilizers. A clover and grass mixture was grown every fourth year and probably supplied enough fresh organic matter to maintain the physical condition of the soil. Higher yields were obtained from the artificial fertilizers. It can be concluded that at least in northern latitudes manure does not provide all of the plant nutrients needed and fails to provide any plant nutrients or growth substances that cannot be supplied by artificial fertilizers.

The chief benefits from manure are indirect. The humus it supplies improves the physical character of the soil by increasing its capacity to take in and hold water, its aeration, and temperature relations. It favors the biological activities of lower organisms that work over the stock of organic residues and plant nutrient-bearing minerals in the soil and make them more usable. The physical properties of soils that are too heavy or too light are improved by an increase in the humus content.

Gardeners and nurserymen who use large amounts of manure know its beneficial effects on the soil. Farmers who apply limited amounts may not see marked changes in the soil. Without a doubt, however, the incorporation of moderate amounts of coarse organic matter into the soil is important. The protection from beating rains and evaporation afforded by manure used as topdressing improves the tilth and reduces erosion.

In an experiment at Zanesville, Ohio, runoff and soil loss were measured from two corn plots, one top-dressed with manure and one not, on a 12-percent slope of Muskingum Silt Loam. Erosive rainfall was heavy the first year of the experiment. Soil loss from the untreated plot from late June until harvest was 41 tons an acre. Soil loss from the plot topdressed with manure was 1.4 tons an acre. Runoff loss of rainfall from the topdressed plot was less than half of that from the unmanured plot.

Maintenance of the humus content of the soil is not merely a matter of incorporating organic matter, such as straw and cornstalks, the composition of which differs greatly from that of stabilized soil humus, which results from the accumulation of centuries of biological activity in the virgin soil. Such materials as straw contain relatively less nitrogen in proportion to carbon, in the form of easily decomposed carbohydrates, than does humus; the carbon-nitrogen ratio is about 50 to 1, compared with 10 to 1 for humus.

When unhumified organic matter with a wide carbon-nitrogen ratio undergoes biological decomposition, the organisms that carry on the processes require nitrogen and the other fertility elements, which they build into their cell substance, just as higher Plants do. The straw has too little nitrogen to supply what the organisms need to decompose this raw material. Because they must get more nitrogen from the soil, they and the crop compete for it. That explains the bad effect often noted from Plowing under straw or fresh manure containing a lot of straw or sawdust. It can be prevented by adding 0.5 to 1 percent of available nitrogen, based on dry weight of straw.

Good manure, however, contains enough quick-acting nitrogen to take care of the decomposition of a normal amount of straw and also furnish some for the immediate needs of the crop. Thus it is necessary to conserve the nitrogen of farm manure, for it is a direct plant nutrient and is essential to the formation of humus.

The reducing action of manure decomposing in the soil aids in making available iron and manganese, present in all soils but sometimes unavailable under excessively oxidizing conditions. The soluble organic matter supplied by manure is believed to aid in keeping iron and phosphates in solution, thus promoting their availability to plants. Some persons believe grain and forage grown with animal manures have greater nutritive qualities than those grown in the presence of mineral fertilizers. Experiments provide no data to justify this hypothesis, however.

MANURE FROM DIFFERENT classes of animals varies in value. Manure from grass-fed animals, growing stock, and milk cows is less rich than manure from animals being fattened or from work animals liberally fed on concentrates. The reason is that the constituents of the excreta are derived from the food. Passage through the animal can add nothing to the total amount of the fertility elements.

Growing animals and milking cows utilize considerably more of the nitrogen, phosphoric oxide, calcium, and so on of their food for flesh, bone, and milk than is retained by mature stock on maintenance rations or fattening. They need liberal feed to get the carbohydrates and proteins necessary to transform energy from food into work or stored fat, but less of the nitrogen and minerals are retained in proportion to the greater amount of food.

The constituents of feedstuffs actually utilized are the carbohydrates and fats for energy, the nitrogenous proteins for energy and tissue building, and the mineral constituents for bone and milk and body processes.

Digestive processes depend on the action of enzymes, which the animal secretes and which dissolve and break down the complex molecules of feed materials into more simple soluble substances carbohydrates to sugars, proteins to amino acids, and fats to fatty acids. In this state the food can diffuse into the blood and be carried to all parts of the body.