A) cowdung, manure
B) Anabaena and Azolla
C) chemical manure
D) All of the above
Correct Answer: B
Solution :
Biofertilizers are micro-organisms, which bring about nutrient enrichment of soil by enhancing the availability of such nutrients like nitrogen and phosphorus. They do not pollute environment and are renewable. The various biofertilizers are (i) Free-living nitrogen fixing bacteria eg, Azotobacter, Beijerinckia etc. (ii) Symbiotic nitrogen fixing bacteria, eg, Rhizobium species in root nodules of legumes. (iii) Nitrogen fixing cyanobacteria, eg, Anabaena. Azollae is symbiotic Na-fixer in small aquatic fern. Azolla pinnata is inoculated to rice field. (iv) Mycorrhiza is symbiotic association between fungus and plant roots. They are of two types ie, ectomycorrhiza and endomycorrhiza. Manures are fertilizers of biological origin. They are of three types (i) Farmyard manures are most valuable organic matter applied to soil. These consist of a mixture of cattle dung and crop residue. (ii) Composite manure is used to supplement or replace inorganic fertilizers or livestock food. It may also be used for energy production or other purposes. (iii) Green manures Crops are grown to improve the soil and are filled under rather than harvested. They add organic matter to the soil and held nutrients, eg, legumes. Chemical fertilizers are man made fertilizers. They are used to supply different nutrients to soil like urea.
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