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Function of mulch

A mulch is a covering layer of material applied over the surface of land. The layer of mulch creates a buffer between the soil and aerial environment. Mulches areused for many different functions and may be composed of many different materials

Water Conservation

This practice is perhaps the most common reason for applying mulches. Water rises naturally in the small pores and channels of soils through capillary action. A mulch breaks up the capillary rise at the soil surface and inhibits evaporation of water into the atmosphere. Also, the soil is protected from drying by direct sunlight and wind. Mulches decrease runoff over the soil surface and enhance penetration of water into the soil.

Weed Control

Mulches for weed control should be thick enough or impervious enough so that weeds cannot grow through them. Straw or sawdust mulches should be 2 to 4 inches thick after packing. A similar mat of hay can be used, but it may contain crop or weed seeds that will infest the soil. Maintenance of a several-inch-thick
layer of hay helps to avoid the problem with weeds.

Temperature Regulation

Temperatures in soils are stabilized by the insulating effects of thick layers of organic matter. Plastic layers warm soils and facilitate early planting of crops in the spring. For winter protection of plants, thick layers of organic matter are used. These materials should be applied after the ground has become cold after a few light freezes or after it has frozen. Their purpose is to keep the ground cold and to prevent the action of freezing and thawing in the soil

Sanitation
Mulches will keep produce cleaner by keeping mud from splashing on upright or fallen plants. The mulch will lessen disease infection on foliage or fruits that come in contact with the ground.

Ornament

Many mulches enhance the appearance of plots as well as provide other useful functions. Bark mulches are valued highly for their ornamental value. Cocoa hulls, cottonseed hulls, or buckwheat hulls make attractive mulches

Insect Control

Reflctive mulches, such as aluminum foil, foil-coated paper, or aluminum paint applied to plastic or directly to the soil have been demonstrated to repel insects. These materials are effective in repelling aphids that carry viral diseases that infect squash. Apparently, the reflective surfaces confuse the insects so that they do not land in the plots. Reflctive white plastic mulches also have this capacity.

Plant Nutrition

Manures, composts, hulls, leaves, and other plant residues contain plant nutrients, and suffiient nitrogen and potassium may leach from these mulches to fertilize a crop in a current season. Other nutrients generally are too low in concentrations in the mulch or too immobile in the mulch and soil to provide much nutrition to a crop in   one season.

Leaching Control

On sandy soils, plastic mulches have been employed to inhibit leaching of fertilizers. In this use, mulch is applied over, sometimes elevated, beds in which concentrated bands of fertilizers are placed. The water table should be high in these soils; otherwise, the soil may become droughty

                     Functions of Mulches and suggested Materials
Water conservation: Straw, hay, sawdust, woodchips, composts, manures, dust, plastic
Weed control: Straw, sawdust, woodchips, leaves, black plastic, paper, hay, composts, manures
Temperature regulation: Plastic (soil warming), organic materials (soil insulation)
Sanitation: Plastic or organic materials
Erosion protection: Organic materials, plastic, burlap, stones, gravel
Plant nutrition: Composts, manures, hulls, leaves, plastic (to prevent leaching)
Insect repulsion:Light plastic, aluminum foil, foil-covered plastic or paper
Ornament: Bark, woodchips, sawdust, peat moss, hulls, sand, gravel, dust