Drought took its toll on the trade balance last month. Exports exceeded imports by $157 million, equivalent to 4 per cent of exports.
But it is normal for April's trade flows to be in the black - and the surpluses had averaged 10 per cent of exports over the previous five Aprils.
The surplus disappointed market expectations of more than $500 million.
The annual trade balance, which had been improving, deteriorated to a deficit of $694 million, $179 million wider than in the year ended March.
Dairy exports, which had shrunk 18 per cent in March on a seasonally adjusted basis in both volume and dollar terms, fell another 7 per cent in volume terms last month.