We applied raw milk to pastures, berry trees and garden patches for a few years. It's the fats in the milk that are easily broken down into sugars/carbon that make a great food source for the microbes. With raw milk from a grassfed cow you get a lot of beneficial enzymes/microbes as well, according to research done by the late Terry Gompert at the Univ of Nebraska @ Lincoln.
After a visit with Terry when we spoke at the same conference in Alberta a few years ago, I followed his recipe of 1ga raw milk to 4ga water, and spread it on all sorts of things. Our berries were bigger and sweeter, soil was softer and looser, and bugs were definitely down in the garden. Which is no surprise since bugs can't digest sugars.
It's great for soil, but it's not a silver bullet. One thing we found is that in certain soils you have deficiencies that milk simply can't correct. Sometimes you need a stronger source of Calcium to overcome excesses of things like Magnesium. That's when I use GSR Calcium from South Dakota. Works great.
I've tried soft rock phosphates, liquid fish, compost tea and all sorts of things. Bottom line, there is no silver bullet, but any of these products are far better than putting NPK on year after year after year. NPK feeds the plant, it does not feed the soil. So the growth of the plant takes minerals from the soil, and you are not replacing them. Over time your soil gets worse and worse. You have to add amendments or do crop rotations that include green manure plowdowns or in a pasture setting you have to rotationally graze things properly or you will have issues. Those could range from weeds, invasive plants, declining production or any number of things. They are all a result of not managing for better soil.