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Which one of the following statements is correct?
A
Both Azotobacter and Rhizobium fix atmospheric nitrogen in root nodules of plants.
B
Cyanobacteria such as Anabaena and Nostoc are important mobilizers of phosphates and for plant nutrition in soil
C
At present it is not possible to grow maize without chemical fertilizers
D
Extensive use of chemical fertilizers may lead to eutrophication of nearby water bodies.
Detailed Solution
Chemical fertilisers, mainly nitrates and phosphates, that are used in excess are washed from the fields into nearby ponds, lakes and rivers.
This nutrient enrichment causes heavy growth of algae (algal bloom) and, later, depletion of oxygen in the water. The process is called eutrophication. So this statement is correct.
Rhizobium fixes nitrogen in the root nodules of legumes, but Azotobacter is a free-living nitrogen-fixing bacterium of the soil; it does not live in root nodules.
Anabaena and Nostoc are nitrogen-fixing cyanobacteria. Phosphates are mobilised mainly by mycorrhizal fungi.
Maize, like other crops, can be grown without chemical fertilisers, using organic manures and biofertilisers (organic farming).
So the correct statement is that extensive use of chemical fertilizers may lead to eutrophication of nearby water bodies.
This nutrient enrichment causes heavy growth of algae (algal bloom) and, later, depletion of oxygen in the water. The process is called eutrophication. So this statement is correct.
Rhizobium fixes nitrogen in the root nodules of legumes, but Azotobacter is a free-living nitrogen-fixing bacterium of the soil; it does not live in root nodules.
Anabaena and Nostoc are nitrogen-fixing cyanobacteria. Phosphates are mobilised mainly by mycorrhizal fungi.
Maize, like other crops, can be grown without chemical fertilisers, using organic manures and biofertilisers (organic farming).
So the correct statement is that extensive use of chemical fertilizers may lead to eutrophication of nearby water bodies.