By NBP, Cambodia:
Biogas slurry, or effluent, consists in general of 93% water, 7%
dry matter of which 4.5% is organic and 2.5 % is inorganic matter. The
percentage of NPK (Nitrogen, Phosphorus and Potassium) content of slurry
on wet basis is 0.25, 0.13 and 0.12 while in dry basis it is 3.6, 1.8
and 3.6 respectively.
In addition to the major plant nutrients, it also provides
micro-nutrients such as zinc, iron, manganese and copper that are also
essential for plants but required in trace amounts.
The bio-slurry coming out of the digester has the following characteristics:
- When fully digested, effluent is odourless and does not attract insects or flies in the open.
- The effluent repels termites whereas raw dung attracts them and they can harm plants fertilised with farmyard manure (FYM).
- Effluent used as fertiliser reduces weed growth with about 50%. When FYM is used the undigested weed seeds cause an increased weed growth.
- Composted effluent and effluent used as liquid fertilisers have a greater fertilising value than FYM or fresh dung. This because nitrogen is available in a form that can be immediately absorbed, for some crops it is superior to chemical fertiliser.
If bio-slurry is composted the nutrient value will be added into
it. Digested slurry is an excellent material for accelerating the rate
of composting of refuse, crop waste and garbage etc.
The following table shows the N, P, K values in different types of organic fertiliser (Gupta 1991):
|
Nutrients
|
Compost Manure
|
Farm-yard Manure
|
Digested Bio-slurry
|
|||
|
Value Range in %
|
Average Value in %
|
Value Range in %
|
Average Value in %
|
Value Range in %
|
Average Value in %
|
|
|
Nitrogen
|
0.50-1.50
|
1.00
|
0.50-1.00
|
0.80
|
1.40-1.80
|
1.60
|
|
Phosphorus
|
0.40-0.80
|
0.60
|
0.50-0.80
|
0.70
|
1.10-2.00
|
1.55
|
|
Potassium
|
0.50-1.90
|
1.20
|
0.50-0.80
|
0.70
|
0.80-1.20
|
1.00
|
It can be seen from the above table that digester bio-slurry has
better nutrient values in comparison to other organic fertilisers. The
effect of compost on crop production depends upon the type and condition
of the soil, the quality of the seeds, climate and other
factors. However, application of compost will bring the following
changes to the soil:
- Improvement of the physical structure of the soil.
- Increased soil fertility.
- Increased water-holding capacity of the soil.
- Enhanced activity of the micro-organisms in the soil.
Effluent compost, if stored and applied properly, improves the soil
fertility and increases cereal crop production with 10-30% as compared
to FYM. The application of liquid effluent has proven to be very
successful on paddy, wheat, maize cabbages, tomatoes, etc. The most
responsive crops, however, to effluent compost are vegetables like root
crops (carrots and radish), potatoes, fruit trees and rice (Kharif,
India-1988).
Chart above: The relationship between a biodigester and agriculture in a farming family
The Compost Saving Hut
The evaluation of field experiment in Kompong Cham province
The Extension Worker monitor experimental plot Model Farmer showing the effect of slurry
Model farmers present their field experiments during field visit in Kompong Cham and Tekeo
Rice field with slurry application The discussion during farmers exchange visit
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