I have an abundance of homemade compost. It's made from my own shredded tree leaves, plus kitchen scraps and garden clippings, plus human urine. Is there any reason for me to be buying bags of composted cow manure which are offered for sale at my local nursery? In other words, is composted cow manure in any way better than homemade compost which happens to be made without any manure? What I've been doing in the past is using BOTH the manure and my own compost, e.g. for roses at planting time and also for top-dressing. But it occurs to me to wonder if the manure really adds anything. . .
seems to me that your own finished compost should be equal in value. By the time the cow manure is composted, bagged, stored, shipped, I doubt there is much in the way of unique microbial population. Just my guess.
I agree that your home made compost has every good thing you can expect from bagged manure compost. And you know you DON'T have any persistent herbicides or weed seeds in your own raw ingredients!
If you worry that some heavy-feeding vegetables are not getting as much N-P-K as they need, or you worry about micronutrients, compost won't do it for you unless you can lay down many inches of compost every year. Compost has only small amounts of mineral nutrients, and they are released rather slowly.
Restoring N, P, K or micronutrients to exhausted soil, or to supply some heavy feeder you are growing intensively are valid reasons to add small amounts of chemical fertilizer (20-10-10 or 16-16-16 or like that). Or to foliar-feed.
Or to add medium amounts of organic fertilizers that have more minerals than compost, but less than chemical granules. Blood meal, bone meal, fish emulsion, kelp pellets, greensand.
Just don't go overboard! It is easy to overfertilize and hard to correct. Safer to spray a little something on the leaves, to see if those plants REALLY DO need more nutrients.
Even real nutrient deficiencies may be due to wrong pH or some soil imbalance rather than caused by low levels of the nutrient in the soil. "Adding more" might not make "more available" to the plant.
Many regions have chronically wrong pH soil. I've always lived where soil was too acid, and needed some dolomite lime every few years.
Some places may have saline soil and that may interfere with some nutrients' availability to plant roots. What that needs is to have excess salts leached away, not anything added.
If you have specific deficiencies like Iron or Magnesium or Sulphate, and you're sure of what is lacking, then pick specific remedies like iron Sulphate or Epsom salts.
But you might want to get your soil tested before adding very much of any one thing. And it's good to test your theory by foliar spraying before you start spreading excessive amounts of concentrated fertilizer on the soil.
If you want to address most of the micronutrients all at once without risk of unbalancing the soil, consider rock dust or Azomite.
But constant supplies of compost are likely to keep the micronutrients in supply.