"Synthetic pesticides and genetically modified crops are effective—by choosing not to use them, organic agriculture requires more manually-intensive labor—sometimes as much as 35 percent more. Herbicides used in organic farming are often less effective at eradicating weeds, requiring more physical weeding. Because organic farms don’t use as much fertilizer, cover crops are needed to enhance soil nitrogen levels—which in turn increases the amount of labor time invested in each field."