It's a great way to build the soil. Michael's recommendation of using multi species cover crops is also very good. So long as you maintain the moisture levels of your soil (not saturated, not too dry) and add organic matter it all works. If you look at the thread
https://permies.com/t/57161/Photos-Joseph-Lofthouse-Garden On the third page there are some very good photos of the cover crop Joseph is growing this winter to rejuvenate one of his fields. I know he doesn't use any added fertilizers or manures and farms very successfully in a very harsh climate.
If you are careful of your source and have enough rainfall to wash away salt build up, then manures are ideal for the garden. Be careful of where you get the manures from, though. There are now persistent herbicides that frequently contaminate animal feeds. If you get manure from an animal eating these then you will be applying herbicide with the manure. They'll kill or weaken most garden vegetables.
Organic should always be safe, and if you know the farmer you can ask questions. Many people who don't get certified organic still use responsible management techniques that don't spread these poisons. I buy pastured chicken eggs from a neighbor here and I can't imagine them wasting the time any money for organic certification. I still don't worry about accidental poisoning from them.
Another resource that is now commonly contaminated is straw. I don't know what else to watch. Many of the people here won't bring outside material onto their property because of these kinds of concerns.