Ukrainian grain exports fell sharply to 1.45 million metric tonnes in the 1 - 21 September period from around 2.94 million tonnes in the corresponding period in 2022, agriculture ministry data showed.
The ministry gave no explanation for the fall.
Traders and agricultural unions have said that Ukrainian Black Sea ports being blocked and recent Russian attacks on Ukrainian ports on the Danube River are the main reasons for the reduced exports.
The ministry data showed that Ukraine exported a total of 6 million tonnes of grain so far in the 2023/24 July-June season versus 7.2 million in the same period in 2022/23.
The volume included 2.9 million tonnes of wheat, 2.5 million tonnes of corn and 596,000 tonnes of barley.
Ukraine has traditionally shipped most of its exports through its deep water Black Sea ports.
A deal brokered by the United Nations and Türkiye which had allowed such exports collapsed in July as Russia walked away from it, saying its demands to ease sanctions on its own grain and fertiliser exports had not been met.
Ukraine can currently export limited volumes through small river ports on the Danube and via its western land border with the European Union.
Ukraine is expected to harvest at least 80 million tonnes of grain and oilseed in 2023 and the 2023/24 exportable surplus totals around 50 million tons.
It said 29.8 million tonnes of grain and 7.6 million tonnes of oilseeds had been threshed. The harvest ends late this year, depending on the weather.
The volume included 22.2 million tonnes of wheat, 5.9 million tonnes of barley, 396,800 tonnes of peas and smaller contributions from other cereals.
It also said farmers had harvested 4 million tonnes of rapeseed and 2.4 million tonnes of sunseed.
The ministry has said Ukraine is likely to harvest 56.4 million tonnes of grain this year, up from 55.3 million in 2022.