The figures - based on data collected in August when harvesting of the drought-stricken crop had started in some parts of Spain - put the barley harvest 58.2 percent below the previous year's big crop.
As a result of the smaller barley harvest, the ministry cut its estimate of the overall autumn and winter grain harvest to 8.9 million tonnes, 53 percent lighter than last year's and down from 9.1 million tonnes seen in the previous month's data.
It also trimmed the estimate for the maize crop, which follows a different cycle, to 3.7 million tonnes.