The country's purchasing power with the rest of the world has fallen due to lower dairy prices.
Official figures show the terms of trade, which measures the amount of imports that can be bought with a given amount of exports, fell 4.4 percent in the three months to September, after six successive quarters of gains.
ANZ Bank senior economist Mark Smith said dairy auction prices had halved since February, and that was being reflected in the data.
"We're starting to see some of that come through now pretty loud and clear, particularly with export prices down 4.5 percent but dairy down around more than twice that, so it's very much a dairy story at present," Mr Smith said.
The terms of trade is now 5.9 percent below its all time high in the June 1973 quarter.
Statistics New Zealand said export prices fell more than import prices.
Exported goods fell 4.5 percent, led by dairy and forestry products, which more than offset higher meat prices.
Dairy prices tumbled 11 percent, their second consecutive quarterly fall, with milk powder prices down 13 percent.
Forestry products fell 3.9 percent, reflecting lower prices for pine logs as international demand decreased and stocks built up in China.
In contrast, meat prices rose 4.3 percent, with beef prices rising to its highest level since the March 2002 quarter, while lamb prices also gained.
Excluding dairy, export prices fell 0.9 percent.
Import prices edged down 0.1 percent, with the main contribution from falls in prices of cell phones, televisions and digital cameras, which offset higher crude oil prices.
Seasonally adjusted export volumes declined 0.1 percent, led by declines in forestry, while imports rose 2.7 percent due to gains in capital goods.