These losses can be controlled more or less by care in collecting and storing manure, but other precautions are needed.

Fermented manure spread on a field is subject to losses of ammonia by direct volatilization into the air, especially in warm, dry, windy weather. The better the quality of the manure, the greater the possibility of losses in application therefore the effect of previous care may be nullified from causes too little appreciated.

Workers at the Wisconsin Agricultural Experiment Station measured the rates at which ammonia was lost from fermented cow manure under different conditions. One-half to three-fourths of the ammonia (one-fourth to one-third of the total nitrogen) was lost within 12 hours to 7 days at 68 F. with an 8.5-mile wind an indication of the importance of air circulation in loose heaps, storage in places exposed to wind, forking over fermented manure, and permitting it to dry before plowing under as causes of losses of nitrogen.

THE ADDITION OF antiseptics to prevent fermentation losses has been proposed, but the antiseptics that are effective generally are objectionable.

Fixing agents for ammonia have been more generally advocated. Gypsum (calcium sulfate) has been used for many years, although probably as much to reduce the ammoniacal odor in stables as to increase the value of the manure. Because the carbonate produced makes the reaction reversible, gypsum and similar salts of calcium and magnesium cannot prevent the loss of ammonia by volatilization in drying.

Similar use of superphosphate, which consists principally of monocalcium phosphate and calcium sulfate, has been advocated by some and has much to recommend it. Manure is deficient in phosphoric oxide and requires supplements in order to get the full value of the nitrogen and potash.

Superphosphate added to manure causes chemical reactions that lead to a decrease in the solubility of the phosphorus in the superphosphate. The less soluble phosphorus compounds formed are less available to plants, especially those growing on neutral or alkaline soils, as are the phosphorus compounds originally present in the superphosphate. On some soils, therefore, the saving of ammonia nitrogen caused by adding superphosphate to manure may be canceled by the decrease in value of the superphosphate.

Most experiments, however, indicate that superphosphate mixed with manure is as effective as superphosphate applied directly to the soil.

Research workers at Cornell University obtained manure in which the phosphorus was tagged with a radioactive phosphorus isotope by feeding radioactive phosphorus to a sheep. In a greenhouse test, in which a silt loam soil of pH 6.2 was used, the phosphorus in the manure was shown to be of about the same availability to ryegrass as that from superphosphate. Superphosphate incubated with manure for 22 days was of nearly the same availability to plants as superphosphate applied directly to the soil.

It is not possible to prevent all losses. Even if it is spread daily, the fresh material lies exposed for some time and permits volatilization of the ammonia that is rapidly developed in the first stages of fermentation. It is inferred from data obtained in a 40-year field experiment at the Ohio Agricultural Experiment Station that losses from daily spreading may average very little less than losses that occur with a good method of storage, spreading under favorable conditions, and plowing under promptly.

Losses can be reduced if the liquid excrements are handled separately and water is used to moisten the dung if necessary. On many American farms, however, the value of the nutrients contained in liquid manure does not offset the investment and labor required to give special handling to liquid manure.

The principle to be applied in storing manure to keep down the losses without using chemical preservatives is simple compact the manure to exclude air. This prevents heating with its attendant losses, insures acid fermentation, and prevents leaching and drying. The easiest method of compacting manure is to let the animals do it the well-known deep-stall method of accumulating manure under fattening stock effectively conserves values.

Sanitary regulations applying to the production of market milk prevent the use of the simple deep-stall for dairy cows, but the essential requirement of compacting the manure under cover at the legal distance from the quarters for milk cows may be met.

THE VALUE of manure as a mulching material may be greater than its value as a source of plant nutrients.

In experiments in Ohio, strawy manure used as a topdressing on corn after the first cultivation increased corn yields more than did equal amounts of manure plowed under before planting. The corn crops followed legume or legume-grass meadows in a rotation. The yield differences in favor of top-dressed manure have been greater in drier years than in wet years, an indication of the importance of the manure mulch as a moisture conservation measure. Part of this moisture conservation was probably due to the effect of the manure mulch in reducing runoff. Another part was probably due to the effect of the mulch in lowering evaporation of soil moisture.

A surface mulch of manure will reduce soil blowing on coarse-textured soils. The clumps of manure on the surface of the soil break the force of the wind on bare soil. Such mulches are especially valuable in protecting newly seeded crops.

Freshly shaped and seeded grass waterways should be coated with a topdressing of manure whenever possible. It will reduce soil washing within the waterway and promote a better stand of the new seeding by preventing excessive drying of the surface soil.

The value of manure as a mulch is largely due to the bulk and the undecomposed litter material the nutrient content is less important. Stack bottoms, spoiled hay, and such can be substituted for manure for mulching.

On farms where a critical problem of soil washing or blowing exists and manure is the only mulching material available, first priority on its use should be as a mulch.

Another rule to follow in deciding where to use manure is that the poorer the land, the more valuable the manure. In one experiment in Ohio, an area of soil was desurfaced with scrapers and the topsoil spread over a similar unscraped area of the same size. Each of these two areas and one with normal depth of topsoil were farmed for a number of years with different systems of management, some with manure and some without. The experiment was set up so that the value of manure could be determined on soil with each of the three topsoil conditions. The manure was most valuable on the desurfaced plots and least valuable on the plots with a double thickness of topsoil.

Manure will be of most value on row crops that follow nonleguminous crops. While land is in grass-legume sod, soil aggregation is improved. Soil nitrogen is increased when the legume meadows are turned under. When intertilled row crops follow, the physical condition of the soil usually becomes less desirable, and supplies of available nitrogen diminish. Liberal applications of manure can help to slow down this trend and permit the crops that do not follow legume-grass sods to grow under more favorable soil conditions.

Manure will give greater economic returns on crops with a high acre value. Thus, applications of manure are likely to be more profitable on crops like corn, burley tobacco, potatoes, and vegetables than on crops like small grain or pasture.

WHEN MANURE is used as a topdressing or mulch to help combat soil washing or blowing, the application should just precede the time of greatest hazard. Often that will mean applying the manure fairly soon after the crop has been planted.

Losses of nitrogen by volatilization of ammonia are sharply cut as soon as the manure is covered by soil. Research in Denmark indicated that if manure spread and plowed under immediately is rated 100 in crop-production ability, manure spread and plowed under 2 days later rates as 71, and manure plowed under 2 weeks after spreading can be rated as 49. Spreading manure just ahead of a tillage operation that will incorporate it with the soil, therefore, is preferred when the manure is not used as a topdressing.

Other research in Denmark demonstrated that manure spread and plowed under just before the crop is planted is more effective than manure spread and plowed under at earlier dates. A farmer who uses such a plan of manure management should keep in mind, however, that factors other than the need for conserving nutrients in manure may be more important in determining the best time for plowing.

When dairy barns of the stanchion type or farrowing sheds for hogs must be cleaned often, a manure carrier or gutter cleaner that empties directly into the spreader saves work. Such a setup frequently makes it convenient to spread manure on frozen or snow-covered ground. Studies in Vermont showed that this practice resembles partial drying insofar as its effect on losses of ammonia through volatilization are concerned. These losses of nitrogen, therefore, will have to be balanced against the labor-saving features of the system.