Study has shown composted manure can increase crop yields and disease resistance
A striking finding of the study was how crops responded to compost in dramatically different ways. Few field experiments have compared the effects of compost on crops planted into the same plots. Interestingly, in 1998 the beet crop responded strongly to both composts and the NPK control. In contrast, the carrot crop planted six feet away responded most strongly to the goat manure compost. The mechanism remains a mystery, one of the many as yet unanswered questions about compost management.
Experiment with your garden and your soil, compost or amendments to find what works.