Background and methodology:
The goal of this study was to assess the applicability of stable nitrogen isotopes as a screening tool to differentiate between organic and conventional growing conditions of various vegetable crops. Nine different types of organic vegetables were selected from an organic grocery store and their conventionally grown counterparts from a chain supermarket selling mass-produced vegetables in Lower Hutt, New Zealand. All organic produce was labeled and certified as organic. Conventionally grown (nonorganic) vegetables were selected from bulk produce display areas at the supermarket. Faster growing vegetables (such as tomatoes, peas, broccoli, cucumber, and zucchini harvested at maturity of < 80 days) were compared to slower growing vegetables (such as pumpkin, eggplant, potatoes and corn that are harvest at maturity of > 80 days).
Findings:
In general, organic produce had more positive isotope values and conventional produce had less positive isotope values. The faster growing vegetables showed the biggest isotopic difference. Slower growing crops such as eggplant (90-100 days to harvest), corn and pumpkin (100-120 days to harvest) had the smallest isotopic values.
Stable nitrogen and carbon isotopes can be used as a rapid, low-cost screening tool to identify the organic growing regimen of vegetables (especially those with faster growth rates of <80 days) from their conventionally grown counterparts. For slower growing organic produce (with a maturity time to harvest of >80 days), this technique does not distinguish between the two growing regiments with as much certainty. Further tests would be required to understand isotopic variations and fractionation effects between plants and soil over time. The technique also appears to be useful for detecting potential over fertilization with organic manure, raising issues of sustainability in organic farming practices.
Reference:
Rogers, K. M. (2008). Nitrogen isotopes as a screening tool to determine the growing regimen of some organic and nonorganic supermarket produce from New Zealand. Journal of Agricultural and Food Chemistry, 56(11), 4078-4083. Available on-line at: http://dx.doi.org/10.1021/jf800797w