What is meant by "no change though you lie under the land you used to plough"? his fields have not been touched since he died. life has gone on without him. his horses do not miss him.

The quote given above is by A. E. Housman. This is actually from a poem " The Road of Danger, Guilt, and Shame: The Lonely Way". And based on this metaphor, it means that his fields have not been touched ever since his death. When he died, he was buried on the same field and since then, this land has never been touched.