Composting is the most popular practice for improving soil fertility The process involves mixing various organic material (high and low C/N, wet and dry matter, dung, grass, soil, etc.), allowing for decomposition, and after complete decomposition, using this as organic fertilizer. The main purpose of composting is to make raw organic matter into humus which is most important for the soil and not harmful to plants.
5.4.1 Advantage
Quick Action
Compared with mulch and green manure, compost starts working very quickly – in about 10 days. The organic material in compost is already decomposed during the process (2 – 3 months) and is in a form (humus and nutrients) suitable to plants.
Healthy Fertilizer
Good compost is a healthy fertilizer and creates healthy soil. One of the main benefits of this method is it avoids mixing raw organic matter with soil by decomposing the organic matter completely first. Raw material is harmful to plants and causes pest problems (Chapter 5.1).
Uses Locally Available Resources
Any organic matter can be used to make compost. Even waste matter, which cannot be used on land directly, can be used. This method also promotes use of locally available resources such as Kochuripana (water-hyacinths) which are available in huge amounts in Bangladesh. Most farmers regard Kochuripana as a problem and expend a lot of labour to remove them (sometimes by firing) from the land. If they realized that Kochuripana is rich in minerals and makes a very good material for compost, as well as realized the advantages of compost, they would compete with each other to use it.
5.4.2 Disadvantages
Amount of Organic Matter Required
The necessary organic matter for one acre per year is about 8 ton or 8,000 kg. If a farmer wants to supply that amount of organic matter through only compost, a huge amount of organic matter is needed. It is almost impossible for most farmers in Bangladesh to gather this much as organic matter (e.g. cow dung, crop residue) is also required for fuel for cooking and other purposes as well. To deal with this it is necessary to find alternative fuel sources (multi-purpose trees) and use other fertilization methods (green manure, and mulch) with compost.
Nutrient Loss
During the process, some nutrients are lost to sun heat, rainfall and wind. To check this loss, the following points should be considered:
1. site selection (under tree canopy, roofing)
2. proper processing including appropriate timing, turning and completing within 3 months
Labourious
The process of compost is quite labourious as it involves collecting material, making the compost, turning the compost pit and carrying the compost to the field. Therefore it is recommended that most organic matter be returned as mulch and unsuitable material be used for compost.
5.4.3 The composting Process
The followings are some important points for making good compost:
Mix dry and wet matter with soil
It is important to mix dry and wet matter with soil in order to provide the micro-organisms which help good decomposition. The aerobic bacteria which mainly carry out the composting process also require sufficient water and air. The appropriate ratio of each material is 6 (dry matter): 3 (wet matter): 1 (soil), Dry material has little water content and usually high C/N ratio which decomposes slowly.
Examples are rice straw, other crop residue, dried water hyacinths, sawdust and tree leaves. Wet material has high water content and usually low C/N ration which decomposes quickly. Examples are cow dung, other animal dung, kitchen waste, leguminous grasses and leaves of leguminous tree.
Balance compost material
All organic matter has a C/N ratio. For instance, rice straw is 60 and cow dung is 25. Material with a high C/N ratio decomposes more slowly than that with a low C/N ratio. Mixing the two is important. Micro-organisms work most effectively when the C/N ratio of the total organic matter is around 40 (e.g. mixing equal amounts of rice straw and cow dung).
Turn compost pit twice every 3 weeks
To make good compost it is important to turn the compost pit twice every 3 weeks in order to supply air to the micro-organisms. This also allows observation of the compost (moisture, progress of decomposition, etc.) and introduction of any control measures needed (e.g. water, drying).
Good compost smells good, is black brown in colouor and has a regular consistency with no trace of the original material.
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