Mulching:
- Mulching refers to spreading of dried leaves hay, straw, or any other organic (Plate 4.1b) and inorganic materials (Plate 4.1a) around the tree basin to cover the soil surface. Plastic mulches can be effectively used.
 Plate 4.1a: Black polythene (left); Plate 4.1b: Dry grass (right)
- A wide variety of materials can be used as mulches, which are broadly classified as organic and inorganic mulches.
- All the organic residues viz. straw, hay (Plate 4.1b), crop residue, leaves, saw dust and organic wastes viz. farm yard manure, poultry manure, spent mushroom compost etc. and inorganic mulches viz. black polythene can be used as mulches.
- In some arid fruit growing areas, pebbles can be used in the event of non-availability of organic material. These mulches act as a surface barrier against evaporation, conserve soil moisture, check weed growth and enrich organic matter to the soil.
- However, mulches should be removed at the onset of monsoon rain.
Advantages:
1. Conserves soil moisture by reducing evaporative losses from soil surface and controls weeds.
2. Organic mulches add organic matter and nutrients to the soil upon decomposition thus save fertilizer requirements.
3. Improves the soil structure, nutrient availability and micro flora.
4. Controls soil erosion.
5. Improves water infiltration and controls weed growth due to etiolation.
6. Reduces soil temperature fluctuation.
7. Mulch acts as a cushion for dropping fruits and thus avoiding physical injury.
8. Growth, production, colour and quality of fruits are improved.
Disadvantages:
1. Cost of mulch is high.
2. Dry grass, hay or pine needle mulches are a fire hazard.
3. Mulch may harbor insects, diseases and rodents.
4. Growth may be extended in some seasons through fall with reduction in fruit quality.
Additional benefits of organic mulches:
- Apart from the advantages listed above, organic mulches alsoImprove root growth
- Increase the infiltration of water, and
- Also improve the water-holding capacity of the soil.
- Organic mulch provides an ideal environment for earthworms and other beneficial soil organisms.
- Organic mulches are more useful for warmer climates i.e. valley areas and low and mid-hills areas of Himalayan region, as these keeps the soil temperature cooler by 2-3o C in summer.
Inorganic mulches:
- Inorganic mulches are usually preferred in fruit orchards located in the high hill areas having cooler climate.
- It also helps in raising the soil temperature in summer, required for greater nutrient absorption and roots metabolic activities.
- However, inorganic mulches lack soil improving properties of organic mulches.
How to and when to apply mulch
- Time of application depends on what is expected to be achieved by mulching. Mulching by providing an insulating barrier between the soil and the air, moderate the soil temperature. This means a mulched (organic) soil in summer will be cooler than the adjacent non-mulched soil; while in the winter the temperature of mulched soil may not drop as deeply as otherwise it would have been.
- Around 10 cm thick hay, straw or pine needles are spread over the tree basin areas in spring immediately after completing the tillage operation and applying second dose of nitrogenous fertilizers in the basins. However, about 10-15cm area away from the tree trunk should be kept open, in order to protect the trunk from the damage of any harbouring insect-pests, rats etc.
- Among the inorganic mulches, use of black polythene sheet of 200 micron thickness around the tree basins or in strips is common, keeping sufficient vacant space for working between the rows.
- Mulches can be applied late in the winter after the temperature falls below freezing point but before the coldest temperature arrives. Applying mulches before the coldest temperature may attracts rodents looking for a warm over-wintering site. Delayed applications of mulch should prevent this problem as, hopefully, the creatures would already have found some other place to nest.
Benefits of winter mulches:
- One of the benefits from winter mulching is the reduction in the freezing and thawing of the soil in the late winter and early spring. These repeating cycles of freezing in night and then thawing in the warmth of the sun causes many small or shallow rooted trees (e.g. young trees) to be heaved out of the soil. This leaves their root systems exposed and results in injury or death.
- Mulching helps prevent the rapid fluctuation in soil temperature.
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