Question

How is rhizobium useful to farmers?
A. They help in nitrogen fixation in the soil
B. They help in killing pests
C. They makes the soil airy, soft and fertile
D. They help in pulling out the weeds

Answer 1

Hint: Rhizobium are microbes that are in symbiotic association with root nodules of leguminous plants. They are useful to plants as they enrich the soil with essential nutrients wherever they are present. The leguminous host provides shelter to the bacterium and helps it in carrying out its metabolic processes.

Complete answer:
Before we talk about the answer let us infer about the quality of the soil. Rhizobium is a bacteria that lives in a symbiotic relationship between root nodules of leguminous plants. They fix the atmospheric nitrogen and convert it into soluble nitrates, nitrites and ammonium compounds. Nitrogen fixation helps in increasing soil productivity and soil fertility. The nitrogen gas is fixed from the atmosphere which is made available in their growth and development. When the legumes die there will be a breakdown of nodules and is mixed with the soil making it more fertile.

The rhizobium is released up into the soil where it can infect the new host. There are few strains that make the nodules functional in order to carry out the process. This increases the yield of the crops. This increases the yield and helps in increasing the fertility of the soil. The pest (organisms that cause infection in the crops) and weeds(unwanted plants) can be controlled by the use of pesticides and weedicides.

Thus the correct answer is option ‘A’.

Note: Excess of pesticides usually hastens the fertility of the soil. Nowadays these fertilizers have used that increase the nutrient content of the soil. Nitrogen is one of the scarcest nutrients in the soil. It is a gram-negative strain that helps in fixing up the nitrogen that is used up by the plants for growth and development.