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Biological properties of soil: |
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A variety of organisms inhabit the soil. They decompose organic matter, fix atmospheric
nitrogen, cause de-nitrification and plant disease.
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- Cultivated soils harbour bacterial, actinomycetes, fungi, algae, protozoa, nematodes,
worms, insects and rodents.
- Specific groups of organisms are responsible for specific activities in the soil.
Such activities may be benefici Bacteria.
- They decompose the organic matter and release plant food nutrients like nitrogen,
phosphorus etc.
- Nitrogen fixing bacteria like rhizobium and azotobacter, and phosporus-solublising
bacteria.
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- Nitrosomonas and nitrobacter bacteria, which oxidize ammonia to nitrate and nitrate
to nitrite compounds respectively, the process is called nitrification.
- These are generally confined to the surface 20 to 30 cm.layer and work best when
there is good aeration, a neutral reaction, soil moisture content at about half
of the water holding capacity and temperature between 250 c and 380 c.
- Phosphate fertilization of legumes also helps to increase the yield of green matter
and more nitrogen is fixed to the soil.
- Fungi
These organisms produce microscopic threads called mycelia and are found in the
organic matter of plant roots. Fungi help in breaking down the somewhat resistant
parts of the organic matter like cellulose, lignin, gums etc. A large part of slowly
decomposing soil humus is made up of the dead remains of fungi.
- Actinomycetes
They can grow in deeper layers even under dry conditions of soil, and require less
nitrogen. Their main function lies in decomposing the resistant parts of organic
matter like cellulose.
- Algae
They are microscopic or very minute sized plants having chlorophyll and are usually
found on the surface of wet soils of paddy fields. They help in adding organic matter
to soil, improving the soil aeration and fixing atmospheric nitrogen e.g. blue-green
algae.
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