Question

Why do farmer grow leguminous crops after harvesting of cereals? In short

Answer 1

it is because legumes have rizobium bacteria in their root nodules.this bacteria helps in conversion of atomospheric nitrogen (indoluble)into nitrates and nitrites (soluble)

plants need nitrogenous compounds for their proper growth

legumes are therefore grown to replenish the nutrients of the soil which was absorbed by the previous crop

hope it helps u

and sorry for a long explaination but the concept wouldn't be clear if i had not done that