Mulching involves covering the soil surface with various kinds of organic matter such as weeds, grasses, fallen leaves, straws, etc. The function of mulch is both conservation and fertilization. Less tillage is possible where enough mulch covers the soil.
5.2.1 Advantage
Soil Protection
The sun heat and rainfall cannot attack the soil directly because of the mulch material on the soil surface. The main cause of erosion in Bangladesh is bare soil in agricultural land and strong rain fall in the rainy season. Plowing is also sometimes the cause of the soil erosion. Therefore, mulch with less tillage is a very appropriate and effective soil protection method for this country.
Effect of Mulch Rate on Run-off and Soil Loss
|
Mulch rate(t/ha) |
Run-off(%) |
Soil loss(t/ha) |
0 |
50 |
4.83 |
2 |
19.7 |
2.48 |
4 |
8 |
0.52 |
6 |
1.2 |
0.05 |
*Rainfall 61 mm. On uncropped land
by Vandana Shiva (Staying Alive)
Improvement of Physical Soil Structure
Because the soil surface is covered by mulch, the soil is not compacted by rainfall and not dried up by direct sun light. Mulch develops the crumble structure on the soil surface which increases water holding capacity and keeps optimum moisture in the soil. In the dry season, mulch prevents evaporation and retains moisture. If soil is always covered by thick mulch (above 2 inch or 5 cm), plowing is not necessary.
Gradual Fertilization
Mulch eventually decomposes and disappears. As it decomposes it adds nutrients to the soil. Mulch fertilization is:
1. balanced and rich in micro-nutrients
2. slow and steady in decomposition
3. less wasteful as the decomposition process takes place on the land where the nutrients are needed
Weed Control
Weeding is a major task in agriculture. As mulch reduces the weeds on the land, continuous mulching is an excellent weed control method. At the Proshika farm, more than 2 inch (5 cm) thick mulch controlled nearly 90 % of the weeds.
Simple and Less Labour
Mulching is a very easy method as it simply involves putting mulch material (e.g. grasses) on the soil surface. Furthermore, as mulch reduces the need for tillage, plowing labour is reduced.
5.2.2 Disadvantages
Fungi
In the rainy season, mulching sometimes introduces fungi harmful to plants. This can be minimized however by selecting material such as high C/N ratio grasses and by drying the mulch material before using it. Continuous mulching can also minimize fungi problems by creating a balance of micro-organisms on the soil surface which control the outbreak of harmful fungi. It is recommended that mulching begin in the dry season and continue in the rainy season. At the Proshika model farm, mulching has been practicing for almost 3 years and there are no disease problems caused to date.
Obstruction to Seed Broadcasting
Mulch sometimes becomes obstructive for broadcasting seeds. Thin mulch after sowing is not a problem but thick mulch before sowing is minimized by controlling the thickness of mulch and timing broadcasting of seeds. There is no problem caused to the planting of seedlings.
5.2.3 Mulch Materials
Any kind of organic matter can be used as mulch material including tree leaves, grassed, crop residue, saw dust, etc. Weeds, lemon grass, coconuts leaves, straw, water hyacinths, leaves of multi-purpose trees (Ipil Ipil, Grilicidia, Flamengia, etc.) and compost have been used as mulch material at the Proshika farm.
In selection of mulch material, it is important to consider your particular requirements and the characteristics of the material. If you require soil protection and want to avoid fungi problems in the rainy season, the use of high C/N ratio (high carbon content) material (more than 60 e.g. straw, lemon grasses, coconuts leaves, etc.) are recommended. These last for a long time and fungi do not break out as easily in such material. For soil fertilization purposes, low C/N ratio (high nitrogen content) material (e.g. leguminous grasses, residue of leguminous crop, leaves of leguminous trees, compost, etc.) are recommended.
5.2.4 Living Mulch
Living mulch involves growing a leguminous grass, short in height and with spreading ability as opposed to putting mulch material on the soil. The advantages are:
1. there is no need to collect mulch material
2. very effective and long lasting soil protection
3. leguminous grasses can provide nitrogen to the main crop
In temperate zones, clover is commonly used as living much (Fukuoka uses clover for his rice field and orchard for mulching purpose). In Bangladesh, Khesari (grass pea) can be used as living mulch with a somewhat taller crop (e.g. egg plant) in winter season.
5.2.5 Cover crop
A cover crop is sort of living mulch. It covers the land with vegetation in the hot dry summer season when land is fallow. Advantages are:
1. prevention of evaporation lowering moisture loss
2. uses sun energy to produce biomass (a source of fertility)
3. weed control
Favorable characteristics of a cover crop are:
1. leguminous crop
2. wide spreading (cover big area)
3. strong against heat
Seem (Dolichos Lablab) is a very effective cover crop in summer time (March – May) in Bangladesh. Velvet bean has excellent potential as a cover crop, though it is not common in Bangladesh. (The seeds of velvet bean are available at Proshika farm).
|
