Farmers depend on cheques from Brussels to make up three-quarters of income.
The latest National Farm Survey from agricultural body Teagasc shows income on farms dipped by 9pc last year, with average earnings now standing at €24,060, or less than the average industrial wage.
And the snapshot of more than 83,000 farms showed farming remains highly reliant on direct payments from the EU's Common Agricultural Policy.
The average direct payment per farm was nearly €18,000 last year - which was 75pc of farm income on average and almost 100pc of the income on cattle and sheep farms.
Teagasc economist Dr Kevin Hanrahan raised concerns over the post-Brexit environment, with a potential 10pc drop, or €130m hole, in the CAP budget after 2019.
"The UK is the second largest net contributor to the EU budget," he warned, adding the terms of the "divorce" settlement were far from finalised.
Teagasc economist Dr Emma Dillon said falls in milk prices and poorer crop yields contributed to the drop in income in 2016. Milk prices fell almost 10pc last year, despite production expanding after removing quota restrictions. Four-out-of-five dairy farmers increased production but income still fell 17pc to €51,809. However, a strong "rebound" was expected with an increase in milk prices this year. Tillage farms were hard hit by poor crop yields and prices, resulting in a 10pc fall in average income to €30,816.
Increase in payments under the environmental scheme Glas and suckler cow payments saw direct payments to cattle farmers rise, with income rising up to 4pc. However, the average yearly cattle farm incomes remain low at just over €12,000, and €16,000 on sheep farms. One-in-three farmers works elsewhere off-farm to supplement incomes.