Trash mulch

In the semi-arid regions the tendency is more and more to leave the residues on the surface to serve as a trash mulch. This practice, which is referred to in Chapter 25, favors water infiltration and erosion control, but presents problems in connection with cultivation and sometimes with weed control. The rate of decomposition of the organic residues is less when left on the surface than when plowed under, but their contribution to humus maintenance is not appreciably diffefent. 

Animal manures are sometimes used as trash mulches and merely left on the surface. In such cases decomposition is retarded because of lack of moisture, and some of the ammonia formed may be volatilized. Most of the nutrients are, however, leached into the soil and any losses sustained are balanced against the benefits derived from soil protection against erosion. The more bedding material in the manure, the more effective this type of use is likely to be. 

The term mulch, as used here, refers to any naturally-formed, undisturbed soil covering any material added to serve as a soil cover and to crop residues left in part on the surface as dead or dying materials. This definition is, therefore, broad enough to include essentially all organic and inorganic materials that serve as soil covers. The main emphasis here, however, is on conventional mulches of organic materials, where the soil is usually completely covered to various depths by plant materials added from outside sources. Reference will also be made to stubble- or trash-mulches, where the soil surface is usually only partially covered. Whether the soil is completely or only partly covered, most of the effects produced are very similar, but differ in degree. 

Mulching materials consisting of various kinds of plant materials have long been used by gardeners, fruit growers, nurserymen, and those interested in ornamental shrubs and flowering plants. These materials commonly include such materials as peat, manures, straw, cornstalks, corncobs, sugar-cane trash, leaves, peanut hulls, wood products, and various other kinds of litter. Since such materials must be applied to a depth of at least two inches if weeds are to be kept under control, it is obvious that they are too expensive (at least in terms of labor) for use as full mulches on field crops. 

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