compost (xcept manures) are usually mild an worth the work. Manures are like any chemical, apply after soil testing. Dont just DUMP it over the garden (or in my case , the fields). Many manures are high in one or more of the components and Nitrogen, usually staring out as ammonia or nitrites will quickly denitrify and convert to nitrates and flow to the water table and cause problems. P and K will usually sit and be taken up by plants unless too much is added(Too much K will raise the pH a lot and make clay out of the formerly tilthy soil. P will form all kinds of non-conservative salts. SO, soil testing isnt just a good idea, its necessary.
Having my fields "nutrient mapped" by a soil scientist saves me money nd more than pays for itself. When I bought this farm almost 30 yers ago, the fields were spent an crop yields were supported by over dumping of horse, pig, an cow manures. SInce then, Ive been managing nutrients by a good sense program and my yields have gone way up (For everything except alfalfa and hard wheats since we are a humid area and great alfalfa is grown in really dry areas where the stuff is irrigated in 160 A rounds.
Micronutrients are very important too. We manage and map our Mo an Se. Se is a micronutrient that lambs need to help them when they are first born. Sheep in our area can bring lambs with "white muscle disease" where the lambs cant stand up and can often dies if Selenium isnt dosed to them.
Also, Copper must be managed.