Public discussions of organic farming, particularly in the news media, tend to be sharply polarized. Advocates insist that conventional farming exhausts the land and is unsustainable. Critics question the wisdom of farming with manure, and suggest that switching to less efficient methods is unethical when so many people in the world are hungry.
These debates tend to be heated in the scientific literature, too, with representatives of each point of view finding studies that back them up. Evidence can be produced to show that organic farms have higher yields or lower yields, produce more water-fouling nitrogen runoff or less. The resultant morass makes it tough for farmers and policy-makers to pin down the relevant facts.
This doesn't mean that the studies are necessarily flawed. It simply reflects the complexity of the systems being studied, and the number of variables involved. Straight comparisons of organic and conventional practice can often be misleading. Organic and conventional growers generally use different strains, for example, emphasizing pest resistance and yield, respectively. And organic farms change year to year, with yields improving and runoff decreasing over time as organic matter builds up and weed seeds disappear.