Barking comes as naturally to your dog as talking does to you. The difference is that, unlike your pup, you probably don’t talk all the time or at the most inconvenient of moments. Dogs bark for many different reasons, including just because they like the sound of their own bark, so it would seem. The problem is that your dog seems to be unable to control himself and when he barks incessantly in the barn, it can cause other problems besides too much noise.
The funny thing about training your barn dog to be quiet is that in most forms of training, your pup must already have been taught to speak on command or you will have to include this in the current training regimen. Oddly enough, teaching him to be quiet is easier to do while you are teaching him to speak.
Working around the barn, there may be times when you need your barn dog to bark such as when someone is approaching, he sees something wrong like a fire, or he needs to get your attention. But, even at these times, he should be speaking in short controlled bursts rather than continuous uncontrolled barking.
This is where teaching him to speak and be quiet on command at the same time can make the whole job a lot easier. You may need to train him away from the barn environment at first and once he has mastered the 'quiet' command, bring him back inside the barn to make sure he will behave there as well. It is far easier to train your pup in a quiet environment first and then move to the noisy barn environment.
As far as supplies go, you really don't need much besides time, patience, your dog, and a large supply of his favorite treats. However, your barn dog should have already mastered the basic commands of 'sit', 'stay', 'come', and 'down'. A dog that has already mastered these commands will be much easier to teach more advanced behavioral skills to. As always, you will need plenty of patience and time for this training or you may find success is always just out of reach.