PDF chapter test TRY NOW

Look at the diagram given below and answer the following questions.

Soil fertility is increased by bacteria. How?
 
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a. A dark-coloured, organic material formed by microorganisms acting on these dead and decaying plant parts is called _________.
 
b. Humus _________ as it contains mineral salts that mix with the soil.
 
c. Plants such as _________ and bacteria like _________ are also widely used in agriculture to fix nitrogen in the soil.