Question

how is grazing food chain comnected with detritus food chain

Answer 1

because detritivores are the primary consumers and when leaves have fallen on the earth's surface then these are eaten by microorganisms such as Bacteria, Fungi, Protozoan, etc .
after this, these help to plants for growing then after sometimes such plants shed their leaves and again these are eaten by microorganisms, thus the grazing food chain conneted with detritus food chain.