Deputy Prime Minister Barnaby Joyce says the Nationals will "drive a hard bargain" in the next Parliament, including a likely extra position in cabinet, but that he wants to keep secret the conditions of a written agreement to be signed with the Liberal Party.

When Malcolm Turnbull was elevated to the prime ministership last September he signed a new Coalition agreement with then Nationals leader Warren Truss.

Although never released publicly, the agreement was widely reported to include support for a new "effects test" in competition law, a plebiscite on same-sex marriage, more support for stay-at-home mothers and the return of the water portfolio to the Nationals.

Asked what he would be pushing for under a new agreement with Mr Turnbull following the election, Mr Joyce told Sky News on Sunday: "The first aspiration is the agreement remains confidential. That's aspiration one, two, three, four, five and six."