Background and methodology:
Many studies have compared the nutritional values of organic and conventional foods. The strength of this study was in its exploration of the mechanisms underlying the differences found between mineral concentrations in organic and conventional grain. In organic management, particularly the elimination of soluble fertilizers often is claimed to enhance grain mineral concentrations. T his study examined grain from wheat on paired organic and conventional farms in two sets of experiments: (1) four pairs of commercial crops, and (2) fertilizer experiments on one farm pair in which no fertilizer application was used, compared with 40 kg/ha of P as either relatively insoluble reactive phosphate rock or more soluble superphosphate. All wheat was grown following a two- to six- year legume-based pasture phase.
Both conventional management and the superphosphate treatment greatly increased yields but reduced colonization by mycorrhizal fungi. While only minor variations occurred in grain N, K, Mg, Ca, S and Fe concentrations, conventional grain had lower Zn and Cu but higher Mn and P than organic grain. These differences were ascribed to: soluble P fertilizers increasing P uptake but reducing mycorrhizal colonization and thereby reducing Zn uptake and enhancing Mn uptake ; dilution of Cu in heavier crops ; and past lime applications on the organic farm decreasing Mn availability. These variations in grain minerals had nutritional implications primarily favoring the organic grain, however, organic management and, specifically, elimination of soluble fertilizers did not induce dramatic increases in grain mineral concentrations. This study indicates that some aspects of organic management can affect the nutritional value of produce to differ from that of conventional produce can be explained using conventional scientific knowledge and processes.
Ryan, M. H., Derrick, J. W., and Dann, P. R. (2004). Grain mineral concentrations and yield of wheat grown under organic and conventional management. Journal of the Science of Food and Agriculture, 84(3), 207-216. Available at on-line at:http://dx.doi.org/10.1002/jsfa.1634.