Yield per acre
(Palmer, 2012) reviews (Seufert et al., 2012). (Seufert et al., 2012) is a meta-analysis examining 66 previous studies.
(Palmer, 2012) describes the strength of a meta-analysis:
In a meta-analysis, a researcher compiles all of the studies on a particular issue, usually discarding those that are methodologically unsound, then finds a statistical method with which to combine them. Ultimately, a meta-analysis turns a series of smaller studies into a large study, which, if done right, carries more persuasive heft and can bring real clarity to disputed scientific issues.
(Seufert et al., 2012) say:
Although several studies have suggested that organic agriculture can have a reduced environmental impact compared to conventional agriculture, the environmental performance of organic agriculture per unit output or per unit input may not always be advantageous.
There are many factors to consider in balancing the benefits of organic and conventional agriculture, and there are no simple ways to determine a clear ‘winner’ for all possible farming situations.
However, with respect to the question about yield, the conclusions are clearer.
Our analysis of available data shows that, overall, organic yields are typically lower than conventional yields. But these yield differences are highly contextual, depending on system and site characteristics, and range from 5% lower organic yields (rain-fed legumes and perennials on weak-acidic to weak-alkaline soils), 13% lower yields (when best organic practices are used), to 34% lower yields (when the conventional and organic systems are most comparable).
In short, these results suggest that today’s organic systems may nearly rival conventional yields in some cases—with particular crop types, growing conditions and management practices—but often they do not.
(Palmer, 2012) rephrases:
Among wheat, corn and other cereals, organic farms were 26 percent less productive, while organic vegetable growers turned out 33 percent less food per acre than those who used pesticides, herbicides and synthetic fertilizer.