THE ENGLISH word mulch has been used since the 17th century, is probably derived from the German vernacular “Molsch” meaning soft or beginning to decay. Mulch is a material applied to the soil surface to prevent loss of water by evaporation, to suppress weeds, to reduce temperature fluctuations or to promote productivity. It is one of the important agronomic practices for conserving soil moisture and modifying the soil health. Nature produces large quantities of mulch all the time with fallen leaves, pine needles, twigs, or any other organic material. It is a source of highly stable carbon that increases organic matter, microbial activity, water holding capacity, nutrient holding capacity, and total nutrient availability. Mulch decreases compaction, water runoff, soil erosion, weeds and evaporation.
Types of mulches:
Organic mulch is made of natural substances such as bark, wood chips, leaves, pine needles, or grasses. These break down gradually to release nutrients into the soil and help to improve its structure. Inorganic mulches are gravel, pebbles, plastic. Non-biodegradable mulches do not boost the fertility or structure of the soil, but they suppress weeds and conserve soil moisture. Before applying plastic mulch, incorporate all fertilizer. Chemical mulches are sprayed on soil surface such as asphalt, resins, and long chain alcohol (hexa-decanol). Living mulches is growing of spreading type crop between the rows of main crop.eg cereal with clover or grasses.
Selection of proper material:
Grasses, leaves of plants, manures, wood chips, bark, garden waste are usually acceptable materials for mulching while meats, bones, large branches, plastics are not suitable.
Effects of mulches:
It is noted that 4-inch dust mulch can conserve the soil moisture up to 30-40%. The Early Roman gave the idea about the stone mulching; china is vastly using pebbles in field as mulch for soil conservation. If mulch is not properly maintained, it will not always increase the yield of crop. It is also noted that the effect of mulch in promoting infiltration during the rains is much greater than its effect after the rain. The force delivered to soil by an inch fall of rainfall is equivalent to that of about 10 ordinary farm tractors cultivating the land. Mulching causes a great reduction in runoff and erosion. Mulches raise temperature during winter and lower them during summer.
Mulch after decomposition adds more organic matter content than does plowing on the same amount of plant residues. Stimulation of micro-organism by stubble mulching improved aggregate stability and infiltration. Mulching greatly increased earthworms population and consequently aggregate stability in the top eight inches of soil. Mulches increase the infiltration rate and earthworms population in the soil. Mulches Improved plant root system which ultimately Influence the utilization of nutrients. It is noted that if mulching should be repeated for several years, 4-5 ton of wheat straw provide significant amount of plant nutrient. Mulch acts like a dug in organic manure. Mulches increases or decreases pH depending upon the pH of mulches.
For agriculture purposes, mulch should have a C:N ratio of 20-30:1. Narrow C:N ratio leads towards fast decomposition of organic matter through mineralization. If there is wider C:N ratio, immobilization leads towards slow decomposition of organic matter.
What do mulches do for the plant growth?
Mulches play role for plant growth by helping to prevent soil erosion. It adds organic matter to the soil. Mulch feeds soil life and improves soil structure by adding nutrients to the soil. It also helps in decreasing water loss due to evaporation. A good mulch also works against weeds.
Limitations in mulching:
Some organisms like ants and termites proliferate too much under mulches which may cause a great damage to the crop. When crop residues are used for mulching, in some cases there is a risk of sustaining pest and diseases. When C rich material is used as mulch, there is a risk of nitrogen immobilization. Major constraint for mulching is the availability of mulch material.
The author is scholar at Department of Agronomy, University of Agriculture, Faisalabad, Pakistan.
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