Define humus and state its function.

How can we prevent the loss of topsoil?

Which of the following is the major factor in deciding soil structure?

Sehaj tried to set up a small kitchen garden in his backyard. However,the soil was sandy and unsuitable for growing vegetables. Within seven days,he solved the problem and started planting seedlings.
$(a)$ Why was the soil in Sehaj's backyard unsuitable for growing vegetables?
$(b)$ What could be the solution he found? Mention any two.

$A$ teacher mentioned organisms that enrich the soil with nutrients. Rahila was curious to know more about them. She searched the internet and learned about $Rhizobium$ bacteria and cyanobacteria.
$(i)$ What are bio-fertilizers?
$(ii)$ Explain how any one of the organisms mentioned above enriches the soil with nutrients.
$(iii)$ Why was Rahila curious to get more information?

What is soil erosion?