They knew that the use of plant and animal wastes would return nutrients to their soil and enrich their farmlands.
(the use of plant and animal wastes; enrich; their farmlands) (They; knew; that the use of plant and animal wastes would return nutrients to their soil and enrich their farmlands)
the use of plant and animal wastes They
enrich knew
their farmlands
that the use of plant and animal wastes would return nutrients to their soil and enrich their farmlands