Is it organic or not?(resulting from these reactions are usual...)

Date:2/1/2008

resulting from these reactions are usually enriched or impoverished in 15N in comparison with the original. The N in synthetic N fertilizers is derived from atmospheric N2, and this process results in little change in the original atmospheric N isotope ratio but, by contrast, nitrate derived from animal manures (typically used in organic farming) can have greater values signifying a 15N enrichment above the original 15N/14N ratio in starting N2. This is significantly different from the fertilizer N isotopic value, and plants grown with different fertilizer sources of N can be identified.

15N-values (stable isotope abundances expressed as the relative difference of the isotope ratio from that of an international standard in parts per thousand), were determined in sweet pepper plants under controlled ambient and soil conditions in a greenhouse. Leaves (young and old), stems, roots and fruits were analyzed in plants cultivated organically or with synthetic fertilizer amendments. Therefore, three types of animal manures (sheep, hen or horse) were applied at preplanting, and during the crop cycle half of the plants in each manure zone received only water, and the other plants received chemical fertilizers as commonly used in conventional cultivation. The results of this study showed that (i) use of synthetic fertilizers significantly reduced 15/14N2vsN2atmosphere compared with treatments that only received water; (ii) with respect to the plant organs, old leaves and fruits were more sensitive to the synthetic fertilizer additions with reductions in 15/14N2vsN2atm of 24.1 and 27.8%, respectively; and (iii) independently of the organic manure used, no additional fertilization (synthetic or organic) was required before 106 days after transplanting with the common dosage of manure, as plant fresh weight was not reduced.

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Contact: Sara Uttech suttech@agronomy.org 608-268-4948 American Society of Agronomy Source:Eurekalert

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