Question

Which one of the following is an example of a biofertiliser?
A. Neem
B. Azolla
C. Urea
D. Potassium
E. None of the above/ more than one of the above

Answer 1

Hint: Biofertilisers are living microbes added to the soil for better cultivation and yield of crops. Bio fertilisers act by mobilising or increasing the availability of various micro and macro-nutrients in the soil.

Complete step-by-step answer:
Using the above hint, let’s look at the options, before approaching the correct answer.

1) Neem is a plant whose derivatives are used as a natural form of pesticide and as an anti-fungal product. As it is not a microbe hence it cannot be a biofertiliser.
2) Urea on the other hand is a well-known fertiliser. Urea is a chemical-based fertiliser with the chemical formula \[CO(NH_2)_2\]. As it is clearly visible from its formula that Urea isn’t any sort of living organism or a microbe, it cannot be a biofertiliser.
3) Potassium is a macronutrient and provides plants with disease-resistant abilities. It is a simple atom of an element and is consumed in various ions forms by the plants or in molecule forms. It cannot be our answer as it isn’t a microbe or living organism, hence it cannot be a biofertiliser.

Now, finally, we have Azolla, which is a water fern and has agronomic importance due to its ability to fix nitrogen. It forms a nitrogen-fixing symbiosis with the cyanobacterium i.e. Anabaena azollae, that is present in the leaf cavity of the fern. It is primarily used in rice cultivation in temperate and tropical regions. It is an efficient nitrogen-fixing bacteria and studies indicate that around 67% of nitrogen fixed by Azolla is released for the use of crops within a short span of 35 days only. Thus, Azolla is a biofertiliser.

Hence, the correct answer is option (B).

Note: Bio fertilisers effectively increase yield in an organic method. It keeps the products free of harmful chemicals and Azolla as a biofertiliser is seen on the rise in rice-producing countries like China, Vietnam, and India.