The Horn of Africa country has suffered a fourth successive year of drought, with rainfall below average and hail and pests contributing to a low harvest.
Simon Nhongo, the UN's resident humanitarian coordinator, said production of cereals and pulses was anticipated to be about 106,000 tonnes this year, compared to 54,000 tonnes a year ago.
"In spite of the fact that it is almost double what it was last year, it is still only 20% of the national requirement," Nhongo said late on Friday.
Last November the Eritrean government and United Nations launched a $163 million joint appeal to feed 2.3 million people affected by drought, but some donors had expressed reservations about how the figures were reached and were reluctant to stump up aid.
"The numbers... for next year have been worked in a very credible way with donors. So far we have had no indication of a challenge to the figures," said Mamadou Mbaye, of the UN's World Food Programme.
Aid workers say people are not starving to death in Eritrea,
but that about 22% of the country's children suffer from malnutrition.
Even those parts of the country producing crops have suffered from a shortage of labour. About 10% of the population is estimated to be in the army, which has been kept well staffed after several years of border conflict with neighbouring Ethiopia.
"In spite of the fact that it (production) is almost double what it was last year, it is still only 20% of the national requirement"
UN's resident humanitarian coordinator
Other factors include a shortage of farming tools and of oxen, whose numbers have been decimated by the drought.
Ethiopia and Eritrea fought a bloody war in 1998-2000 and
tension has increased again since Ethiopia rejected a decision
by an independent Boundary Commission to award the politically symbolic town of Badme to Eritrea earlier this year.