Conclusions
A growing body of sophisticated research over the last decade has compared the impacts of organic and conventional farming systems on soil and food quality. Based on this body of research, some of it carried out in our field experiments and laboratories, we can conclude that:
1. Studies of apple production demonstrate that organically farmed soils display improved soil health as measured by increased biological diversity, greater soil organic matter, and improved chemical and physical properties. Enhancement of soil quality in organic apple production systems can lead to measurable improvements in fruit nutritional quality, taste, and storability.
2. Organically farmed tomatoes have significantly higher levels of soluble solids and natural plant molecules called secondary plant metabolites, including flavonoids, lycopene, and Vitamin C. Most secondary plant metabolites are antioxidants, a class of plant compounds that have been linked to improved human health in populations that consume relatively high levels of fruit and vegetables.
3. Organic farming can, under some circumstances, delay the onset of the "dilution effect." In hundreds of studies, scientists have shown that incrementally higher levels of fertilizer negatively impact the density of certain nutrients in harvested foodstuffs, hence the name, the "dilution [of nutrients] effect." Specifically, tomatoes grown with organic fertilizers maintain constant concentrations of beneficial phenolic secondary plant metabolites and antioxidants, even as fruit grow larger, whereas concentrations of these same beneficial compounds decline with increasing fruit size when the same tomato cultivar is grown using conventional methods and fertilizer.
4. Studies of 27 cultivars of organically grown spinach demonstrate significantly higher levels of flavonoids and vitamin C, and lower levels of nitrates. Nitrates in food are considered detrimental to human health as they can form carcinogenic compounds (nitrosamines) in the GI tract and can convert hemoglobin to a form that can no longer carry oxygen in the blood
5. The levels of secondary plant metabolites in food appear to be driven by the forms of nitrogen added to a farming system, as well as the ways in which nitrogen is processed by the biological communities of organisms in the soil. Compared to typical conventional farms, the nitrogen cycle on organic farms is rooted in substantially more complex biological processes and soil-plant interactions, and for this reason, organic farming offers great promise in consistently producing nutrient—enriched foods.
6. Organic soil fertility methods, which use less readily available forms of nutrients, especially nitrogen, improve plant gene expression patterns in ways that lead to more efficient assimilation of nitrogen and carbon in tomatoes. This improvement in the efficiency of nutrient uptake leaves plants with more energy to produce beneficial plant secondary metabolites, compounds that promote plant health as well as human health.
Commenting on the well-attended symposium, Dr. Preston Andrews said "The work we reviewed over the last decade points directly to two major scientific challenges – We need to understand more fully how soil biological communities process nutrients and communicate to plant roots in order to promote improved quality in organically grown crops. And second, we need better tools to help organic farmers fine-tune their production systems in order to maximize the soil and nutritional quality benefits of organic farming."
The Organic Center's website contains a section on nutritional quality. Reports and presentations posted include the Center's March 2008 comparison of nutrient density in organic and conventional foods, and the "State of Science Review" entitled "Still No Free Lunch: Nutrient Levels in U.S. food supply eroded by pursuit of high yields." This September 2007 report describes in detail the genetic and physiological basis of the dilution effect.
