Comparison of mineral concentrations in commercially grown organic and conventional crops – Tomatoes (Lycopersicon esculentum) and lettuces (Lactuca sativa)

Trace element concentrations and stable nitrogen isotope data (δ15N‰) from tomatoes (Lycopersicon esculentum) and lettuces (Lactuca sativa) were subjected to multivariate analysis in an attempt to distinguish between conventional and organic cultivation. This approach improved the correct classification of tomato samples but appears to have had a limited effect on lettuces. Our findings support the growing body of evidence which suggests that systematic differences in the concentrations of certain elements such as manganese, calcium, copper, and zinc may occur between crops cultivated under organic and conventional regimes possibly due to the presence of elevated levels of arbuscular mycorrhizal fungi (AMF) in soils cultivated organically. We assert that such differences in elemental composition may be useful as ‘indicators of authenticity’. However, we recognise the limitation that this approach may be restricted to horticultural crops where there are significant differences in agricultural practice such as conventional-hydroponic versus soil-grown organic tomatoes.