- Cow manures that are not well-composted should be used sparingly on gardens where crops like potatoes or onions will be grown. E. coli is the big deal, and it is a very big deal.
- Adding too much of a good thing can be bad. Manure is a great source of nitrogen. If the manure is still 'hot' -- not well composted -- you will grow a lot of plant but not many fruit or melons or whatever it is you are growing in your garden.
- Lastly, herbicide carryover in manures is a reality. Some farmers manage their hayfields with herbicides. Cows eat the hay. Cows poop. You gather tht poop up to spread on your garden. Bad things can happen. Take a look at this great publication from NCSU.
I know this may not be the most interesting subject, but be wise when using manures on your home garden!