Mulching is the process of applying a material over the soil surface. Soil is live material whose temperature, just like the human body temperature should be maintained. The ideal temp for avocado is 18-26⁰C. Exceeding this kills the microbes that are desirable in the soil. Maintaining this requires us to mulch. Mulching prevents direct sunlight rays which aren’t good for the soil, that’s why we need mulching. Soil is opaque and when exposed to direct sunlight, raises the soil temperature.

There are two types of mulching; Organic mulching and Plastic mulching.

Organic Mulching is of two types:

  1. We can either use normal grass/weeds cut from the farm and use it to cover around the plant, but this is not so desirable.
  2. The second type is growing specific cover crops like alfa-alfa from a different place, cut and bringing them to use for mulching.
  3. The third option is Live mulching where we grow legumes in between the lines and around the tree, as the legumes start flowering, we cut them without uprooting them and use these offcuts for mulching. This is the most preferable type of mulching.

Plastic Mulching isn’t a new idea. Commercial farmers have used it for decades. Studies have shown that plastic mulch can raise soil temperature, reduce evaporation from the soil, increase dioxide concentration and nutrients, control weeds, protect plants from pests and reduce fruit rotting. The mulch heats up the soil in the dry season and then generates moisture which provides room for pathogenic diseases and also kills aerobic bacteria.

Also important to note is the distance we keep away from the stem while mulching to prevent arthropods from eating up the stem and also reduce moisture build-up. Avoiding exposing the land to direct sunlight through mulching will increase microbial population in the soil, will reduce the water requirements up to 70%, when the organic mulching decomposes and enhances the organic matter/humus in the soil which generally improves the soil fertility and structure.

Pros of mulching

  1. Water conservation
    Mulching conserves water by reducing evaporation from the soil; decreasing water runoff, soil puddling, compaction and erosion; increasing soil permeability; and increasing soil water holding capacity. More water is therefore available during stress and drought periods. This is of cardinal importance for maintenance of tree function during prolonged droughts.
  2. Improved root growth and reduced physiological stress
    Good mulches allow more root growth, both in the litter layer and in the more fertile
    topsoil. Addition of organic matter improves soil structure, porosity and aeration and
    therefore also allows deeper root growth. Avocado roots have a high oxygen
    requirement. More root growth means greater uptake of water and minerals, and probably also
    greater synthesis and translocation of growth-promoting hormones such as cytokinins
    and gibberellins in and from the roots. The net result is reduced stress, resulting in
    more cell division in flowers and fruits, better fruit set, larger fruits, and higher yields.
  3. More mesic soil environment
    It is well known that mulched soils experience less temperature fluctuation, mainly
    because of improved moisture status. This also improves root growth and reduces plant stress.
  4. Mineral nutrition
    Although the primary aims of mulching are not specifically related to organic fertilization,
    all organic mulches decompose to release mineral elements for root uptake. 
    Three mineral elements are regarded as especially important for healthy and prolific
    root growth, viz. phosphorus (P), calcium (Ca) and boron (B). All three have been
    observed to increase under mulch.
  5. Mulches usually reduce weed problems by reducing weed seed germination or reducing
    light levels. However, the opposite may apply with uncomposted mulches infested with
    weed seed.

Cons of mulching

  1. Cost
    One of the main reasons cited for not using mulches is their cost. This applies more to
    mulching materials not available on site. Costs of transport are high due to the bulky
    nature of mulches, and application costs must be considered. These costs must be
    balanced against the increased fruit size (Hass) and yield, and the water and fertilizer
    savings achieved.
  2. Danger of nitrogen ‘draw-down’ (negative period) Mulches with a high carbon to nitrogen (C: N) ratio have insufficient nitrogen for the increased populations of soil microorganisms which help to decompose them. This nitrogen must also be supplied by the soil. The result is a N ‘draw-down’ or ‘negative period’, when the tree roots cannot obtain sufficient N. This can be overcome, at some expense by extra N fertilization. C: N ratios above 100 are very high, so that material such as sawdusts (containing mostly cellulose-rich wood) and uncomposted barks are not good mulching materials.

[Source: www.avocadosource.com]

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