The trial is being conducted in conjunction with the International Cricket Council and will apply to televised matches in the 50-over competition.
Only the captain of the fielding side or the batsman involved will be able to refer decisions, with each team allowed only two unsuccessful referrals per innings.
Alan Fordham, the ECB's operations manager, conceded discussions with umpires on whether to run the trial had received only a "50-50 split" of those in favour.
But he insisted the ECB were right to be dynamic in finding out whether there is a future for increased reliance on technology in the game.
Fordham said: "We are under no illusions this will be an easy trial. If we need to tweak things as we go on then we will.
"While we acknowledge the high standard of umpiring in our domestic game, we believe that the opportunity to explore ways that we can achieve even more correct decisions must be taken and this is the aim of the trial."
The idea of the trial is to cut down on the number of honest mistakes made by the umpires without encouraging fielders to appeal for any half chance.
But it has received a mixed reaction from players.
Yorkshire captain Darren Gough said: "It will be hard work as captain of the side. I think we will rely a lot on the wicketkeeper and we'd probably like to use our referrals against the better batsmen.
"But when you have got players like myself and Dominic Cork bowling, we think we deserve a wicket from every ball we bowl!"
England pace bowler Simon Jones was less enamoured with the move.
"I guess I am a traditionalist," said Jones.
The round-robin competition involving the English counties and the Scotland and Ireland national teams begins on April 22.