Plants need nitrogen to grow well.Though nitrogen is found in air but it cannot be used by plants directly.This nitrogen is converted into nitrogen compound of elements present in earth by nitrogen fixing bacteria into nitrogen compound of elements present in earth by nitrogen fixing bacteria.
There are two types of nitrogen fixing bacteria. They are free living like Azotobacter and Clostridium and symbiotic bacteria like Rhizobium. This nitrogenous compound is taken by plants. When plants and animals die and their body contents are converted into ammino acid byby bacteria. The amminoacid is converted into ammonia by ammonifying bacteria. Some of ammonia pass into air and the rest are converted into ammonium salt.This ammonia salt is converted into nitrate by nitrifying bacteria.There are two types of nitrifying bacteria.They are Nitrosomonas and Nitrobacter.The nitrosomonas bacteria first oxidise ammonia salt into ammino nitrite. The nitrite is again oxidised to nitrate by nitrobacter. This nitrate compound is absorbed by plants.
