''We are pretty happy that we got second, and we are surprised at how well we did, considering the amount of practice we had,'' Ms Walker said.
Ms Walker, who is a shepherd, drove the horses, while Mr Leslie, a contractor, did the ploughing, using a Reid and Gray single-farrow plough.
The horses, Susy and Mac, are owned by David Murdoch, of Middlemarch.
''He is the one who conned us into it,'' Ms Walker said.
A truck driver, Mr Murdoch has four Clydesdales and has been ploughing for about 20 years.
He won the first horse ploughing competition at the national championships about 10 years ago.
''I think I won 20 litres of Universal oil,'' Mr Murdoch said.
''I couldn't enter it this year because of arthritis so I got Sean and Kaye to do it.''
Mr Leslie has ploughed competitively in the past, but not for a couple of years, while Ms Walker had not driven a pair of horses for ploughing for about eight years, although she had been around animals all her life.
Ms Walker said the competitor who originally was meant to take part could not make it, so three weeks before the nationals Mr Murdoch rang her to ask if she would drive the team.
He said Mr Leslie had already agreed to do the ploughing part of things.
''I said: `OK', and then he rang Sean and told him that I was really keen to drive, so he agreed,'' Ms Walker said.
''We didn't find out until later what he had done.''
They had two days at the Palmerston competition to practise and to qualify, and two days of practice at Blenheim [before the nationals].''
She said it was ''an art'' driving, and keeping the horses straight.
''There is so much to watch.''
Mr Leslie said ploughing with a team required thinking about six or seven things at once, making adjustments as they went, then remembering to readjust the adjustments.
''It is very easy to make mistakes,'' he said. ''It could all go wrong in a hurry.''
There were another five teams in the national competition - two from the North Island and three from Canterbury and Marlborough.
Mr Leslie said it was luck that made them successful, while Ms Walker said it was having a couple of good horses that worked as a team that did it.
The horse team has also been used in cavalcades, as well as for weddings and funerals.
Mr Leslie and Ms Walker said they were considering entering more competitions in the area.
Mr Murdoch has also taught them to harness and drive a wagon, as it was done years ago.
Next year's national ploughing championships will be held in Palmerston.