A paper in this week’s issue of Nature and a commentary on Revkin’s DotEarth blog reinforces the argument that a hybrid path in agriculture — incorporating both conventional and organic production practices — gives the best chance of feeding some 9 billion people by midcentury in an ecologically-based manner.
The thoughtful and comprehensive study compares yields in organic and conventional systems and addresses the criticisms of an earlier study by Badgley et al (for problems with the earlier study, see the supplementary discussion in Seufert et al).
The organic agriculture movement has been important because it has brought consumer attention to the overuse of some pesticides and fertilizers. It has also raised awareness of the need to foster soil fertility. But organic farming practices are just part of a future sustainable agriculture. Just like conventional farmers, organic farmers face pests that are difficult to control or environmental stresses that can affect yield. For example, strawberries are highly susceptible to soil born diseases. Currently both conventional and organic growers purchase clonally propagated seedlings that were fumigated with methyl bromide, an insecticide known to increase the risk of prostrate cancer. Unlike conventional growers, organic growers do not use methyl bromide in the field. To reduce infection, they rotate strawberries with another crop, such as broccoli (a less valuable crop). The trade off to the grower is that yields of organic strawberries are lower. And the consumer pays higher prices for organic strawberries. Clearly, we need better methods to control strawberry diseases that will benefit both conventional and organic production.
Although the Seufert et al study shows that yields on organic farms are generally lower than most conventional farms (with important exceptions that the authors discuss), this yield differential will change with time. On the one hand, as Seufert et al point out, improvements in management techniques that address factors limiting yields in organic systems will enhance the yield of organic systems. On the other hand, because organic farmers are prohibited from using genetically engineered crops, they will not be able to reap the benefits of new crop varieties that assimilate nitrogen more efficiently, that are resistant to disease or tolerant of drought. For example, genetically engineered papaya in Hawaii yields 20x more than organic papaya (note, it appears that papaya was not included in the Suefert et al study). This is because there is no organic method to control a devastating viral disease that has infected papaya. At the other extreme, Suefert et al show that yields of other organic fruit and oilseed crops show very little yield differences with conventional crops. Clearly it is impossible to say which farming system is “better”. Each crop and faming system must be evaluated on a case by case basis.
The study points to the need to drop the ideologically charged “organic vs. conventional” debate and instead focus on what matters: the need to reduce the use of the most toxic insecticides, produce food more efficiently using less land and water and to enhance food security in the poorest regions of the world.
