How organic and conventional farming practices impact crop nutrients

University of California, Davis
February 13, 2009

(Elisabeth Kauffman - University of California, Davis)

An overview of several recent studies on the impacts that organic and conventional production systems have on the nutritional quality of food crops was presented by a food scientist from UC Davis, on Feb. 13, during the annual meeting of the American Association for the Advancement of Science in Chicago.

Alyson Mitchell, an associate professor of food science, delivered the talk, titled "Nutrient-Dense Foods: Phytochemicals and Health Benefits," as part of a session about Living Soil, Food Quality, and the Future of Food. Co-author on the paper presented was Eunmi Koh, a postdoctoral fellow in the UC Davis Department of Food Science and Technology.

Mitchell noted that scientists are interested in how different farming practices, particularly pest control and soil fertility management, can affect nutritionally important compounds that occur naturally in crop plants. Such "bioactive" compounds, including certain flavonoids, vitamins and plant pigments, are of particular interest because they are thought to help lower the risk of heart disease, cancer and other age-related diseases.

Plant genetics and environmental factors strongly influence the levels of these compounds in crops; however there is evidence that different methods of growing, storing and processing these crops can also impact the nutritional content of the resulting food products.

Foods that contain higher levels of vitamins, minerals, and bioactive plant compounds provide more nutrition than do foods that are less nutrient dense.

In this paper, Mitchell and Koh explored the findings of several different studies that examined flavonoid levels in tomatoes; compared vitamin C, flavonoid and nitrate levels in organic and conventionally grown spinach; and probed the influence of heat processing on nutritionally important compounds in tomatoes.

More information on Mitchell's research is available at: http://mitchell.ucdavis.edu/

Media contact(s):

• Alyson Mitchell, Food Science and Technology, (530) 752-7926, aemitchell@ucdavis.edu
• Pat Bailey, UC Davis News Service, (530) 752-9843, pjbailey@ucdavis.edu
  

Six encouraging conclusions on the impacts of organic farming on soil quality and the nutritional content of food were reached by a panel of scientists participating in a February 13, 2009 symposium at the annual meeting of the American Association for the Advancement of Science (AAAS). The symposium was entitled "Living Soil, Food Quality, and the Future of Food" and was held as part of the largest scientific meeting of the year that spans all disciplines. The AAAS meeting was held this year in Chicago, Illinois.

The panel of scientists included Dr. Preston Andrews, Washington State University, Dr. Jerry Glover, The Land Institute, and Dr. Alyson Mitchell, University of California, Davis. The "Living Soil, Food Quality, and the Future of Food" symposium was organized and sponsored by Washington State University and The Organic Center. The presentations made by the three panelists and other symposium information are posted below.

Panelists Statement of 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."

Dr. Preston Andrews
Washington State University

Dr. Alyson Mitchell
University of California, Davis

Dr. Jerry Glover
The Land Institute