SylvaGrow® Peat-Free Farmyard Manure is a lovely mixture of anaerobic digestate (which is a by-product of renewable energy production) and up to 20% certified green compost. Very organic and very vegan.
It's perfect for improving soil structure, suppressing weeds and enhancing the water-holding capacity of soil. Along with the nutrients held in the organic matter, this will improve fertility and in turn maximize yields of anything you decide to grow.
Endorsed by the RHS and peat-free, it's one of the best manures on the market at the moment. The only thing you'd need to keep it away from are any acid-loving/ericaceous plants.