Question

what the importance of ploughing?

Answer 1

To turn over the soil and aerate it, as well as bury crop residue and/or weeds.
A plow is used to turn over stubble or a pasture to expose the soil underneath. This allows for further tilling like discing, harrowing and cultivating, to prepare the soil

Answer 2

it allows the root to go deeper into the soil
it helps in bringing nutrient rich soil to the top 
it help the soil to mix with the fertilizers
it helps to remove undesirable plants called weeds
it helps the soil to retain moisture for a long time
it help in trapping air in the soil which is necessary for the root to breathe