Virtually all field work in Vietnam is performed by hand, as can be seen by these farmers separating rice from straw with a very simple motorized threshing machine.
Over my many visits to Vietnam, I have never seen a tractor being used to plough a field. To my knowledge, water buffalos are still used exclusively for ploughing. Planting and cutting is done by hand. The only tractors I have seen are what look like old modified small lawn & garden tractors with their back end removed and hitched to a trailer mounted threshing machine like this. Sometimes they are instead hitched to a low trailer for hauling produce. Look for the open engine and steering wheel on the left side of the photo.