What is the favored way to lighten & amend soil inside a raised bed? My raised beds are aluminum troughs with volumes of 220 gallons. They are 2 x 2 x 8ft. We've been using them for a few years to grow garlic, tomatoes, strawberries, etc, and I haven't really done any maintenance on the soil. I have sent samples to be analyzed to understand the nutrient picture but the soil is fairly dense and clumpy so I'm sure I need to lighten it in some way. We're in Seattle.
One solution I once saw (and it is not my idea, but seems to work) with raised beds is to designate a rotation pattern (say squash, potatoes, corn, beans, roots) and load all the manure onto the year 1 bed. The idea is that squash can tolerate a lot of fresh-ish manure, spuds can handle it after a year, corn after 2 years and so on. So in a given year only the squash bed gets the manure, and you pile it as high as you like without it collapsing and plant pre-germinated potted squash in the top. Over the 5 years the amount of manure diminishes until there is hardly a noticeable layer. There is never a need to turn the manure into the bed soil. Much goodness leaches down from the heaped organic matter into the bed underneath.
From a practical point of view probably best to move say 6 inches of soil from the intended squash bed to the year 5 bed, leaving a good space to start building up the manure.