What are two main themes in the poem "Bullocky," and how has author conveyed them through use of various literary devices?

A "bullocky" is a slang Australian expression for a cattle drover. The poem as a whole can be seen as a somewhat ambiguous tribute to the first white European settlers in Australia, who often made their living as cattle farmers in the hard, dusty outback.

One of the major themes of the poem is the sacredness of the land. By comparing the everyman persona of the cattle drover to Moses, Wright seeks to endow the relationship of the settlers to the land with a quasi-mythical status. The particular literary device being used here is an allusion. These hardy souls are not just making a living; they have crossed into the Promised Land.

There is a hint here that the land was already sacred before the white settlers arrived. For instance, the bullocky, sitting by a campfire at night, hears the sound of centuries of cattle-bells. As only the indigenous population of Australia had been driving their cattle for such a long time, we can hear the echo of their presence in the surrounding landscape. Such an inference would be entirely consistent with other poems in Wright's oeuvre, which often display an acute sensitivity to the land claims of indigenous Australians.

A second theme emerging from the poem is one closely related to the first, that of belonging. We must not forget to whom this land originally belonged. Returning to the faint echo of cattle-bells, it is instructive that Wright refers to the noise as an "uneasy" sound. The presence of the indigenous Australians echoes and haunts the land now occupied by the newcomers from Europe.

The plow "strikes bone beneath the grass." In the poem's overall context, this could be the bone of an indigenous Australian. If that is indeed the case, then the symbolism is striking. The white Europeans' technological advances are literally riding roughshod over ancient burial grounds, profaning the sacred land. However, Wright sees, nonetheless, some hope for a possible accommodation between the two cultures:

O vine, grow close upon that bone
and hold it with your rooted hand.

Wright here employs the vocative, a device used for addressing a person or thing directly. It is a common trope used in rhetoric, which is appropriate here as the author tries to persuade others of the justness of her case. Wright's use of the vocative also relates to the first main theme, namely, the sacredness of the soil, for the vocative is often used in poetry for elevated subjects of great solemnity. 

The vine represents the culture of the white European settlers; the bone, as we have already seen, is that of the indigenous population. Wright is issuing a plea that the white settlers should remain respectful of the land, a land which, morally and culturally, is not really theirs.