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To derive maximum benefit from the use of organic manure, it should be well decomposed and be of
superior quality. It is known that application of under-decomposed manure produces many harmful effects
on soils. It attracts insects-pests due mainly to high crude fiber-content and takes longer time to release
plant nutrients in readily available form. Therefore, it is necessary to know before applying whether the
manure is well matured or not. In practice, well-decomposed manure can be identified easily. It is dark
brown in color with friable consistency, whereas undecomposed manure is of light brown or green color
and lumpy. If air bubbles are seen to evolve in the compost pit, it indicates incomplete decomposition.
When fully digested, the slurry from a biogas plant or composted manure becomes odorless and does not
attract insects or flies.
7.4.1 Composition of Fresh Dung, Dung Slurry 1 and Digested Slurry
Cattle dung is an excellent source of organic fertilizer. The composition of slurry depends upon several
factors such as the condition of cattle dung before mixing with water, breed and age of animal (cattle,
buffalo, horse, elephant, etc.), type of feeds fed to the animals, exposure to sun, anaerobic digestion
process brought about by the bacterial action, etc. Hence an attempt has been made here to compare
different constituents found in the fresh cattle dung, dung slurry and the digested slurry. The relevant data
in this connection have been presented in Table 7.1.
Constituent
Table 7.1: Average Constitution of Fresh Dung, Dung Slurry and Digested Slurry*
Fresh Dung Dung Mixed with Water Slurry
&/kg
% Wet
Base
% Dry
Base
g/2kg
%Wet
Base
%Dry
Base
g/2kg
% Wet
Base
% Dry
Base
Water 800 80 - 1800 90 - 1820 93 -
Dry matter 200 20 100 200 10 100 140 7 100
Org. matter 150 15 75 150 7.5 75 90 4.5 64
Inorg. Matter 50 5 25 50 2.5 25 50 2.5 36
Total N 5 0.50 2.50 5 0.25 2.5 5 0.25 3.60
Mineral N 1 0.10 0.50 1 0.05 0.50 2 0.10 1.40
Organic N 4 0.40 2 4 0.20 2 3 0.15 2.20
Phosphorus 2.50 0.25 1.25 2.50 0.13 1.25 2.5 0.13 1.80
Potassium 5 0.50 2.50 5 0.25 2.50 5 0.25 3.60
Source: van Nes, undated; Based on calculations
Table 7.1 shows that on an average, the fresh dung contains about 20 percent dry matter. Mixing water in
equal proportion before feeding will reduce it to 10 percent. During anaerobic digestion, about 30 percent of
organic matter is decomposed and hence the dry matter will be reduced to 7 percent in the slurry. Nitrogen
content in the fresh dung is about 1 percent. Although no new nitrogen is formed during anaerobic
digestion, its concentration rises to about 1.40 percent due to 30 percent loss of organic matter. In anaerobic
condition most of the nitrogen is converted to ammonium, which is readily available for plant growth.
Whereas in the case of dung, it has first to be biologically transferred in the soil and only then the plant
nutrients get gradually released for plant use. Thus application of undigested organic manure produces
residual effects causing the nutrients to become available to the next crop.
1 Dung slurry means fresh dung mixed with water at the ratio of 1:1
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