But higher prices limited the drop in the value of dairy exports to 0.3 per cent.
Meat exports which had jumped 10 per cent in tonnage terms in March reversed that gain last month and fell 7 per cent by value.
"Intensifying drought conditions over late February and March had led farmers to bring forward livestock slaughter, and this saw a strong increase in meat export volumes in March," said ASB economist Christina Leung.
"However, this has proven to be a temporary spike, with meat exports largely falling back to levels seen at the beginning of this year. Reports of a decline in livestock slaughter in recent weeks means further declines in meat export volumes are likely."
The third of the big three export commodities, forest products, saw volumes continue to grow last month, but that was more than offset by weaker prices and in dollar terms forestry exports fell 12.6 per cent, seasonally adjusted, last month.
"We expect forestry export volumes will hold up as New Zealand becomes the largest supplier of logs to China," Leung said.
This year, China has overtaken Australia as New Zealand's largest export market. It was already the largest source of imports.