NEW INSIGHTS ON THE EFFETS OF DIFFERENT ZEOLITE AMENDMENTS ON PLANTS C-N ISOTOPIC COMPOSITION

The application of inorganic amendments has been recognized as a valuable technique for increasing soil physic-chemical properties (Colombani et al., 2014). Among them, zeolites are known to be well suitable in a wide range of agricultural applications because of their high cation exchange capacity that allow a controlled retention/release of water and nutrients (e.g. NH4 +) (Reháková et al., 2004). The main aims of this study were to verify if natural zeolites amendments can increase the uptake of N from chemical fertilizers and if the N transfer from NH4-enriched zeolites to plants really occurs. The elemental and isotopic composition of plants grown with no zeolite addition (UA) and plants grown on soils amended with natural (NZ) and NH4-enriched zeolites (CZ) (the latter obtained after mixing with pig-slurry) were compared for two cultivation cycles. It is well known that plants δ15N can reflect with a good approximation the δ15N of the main N source in the soil, thus, plants grown under conventional farming (using chemical fertilizers) and plants grown under organic farming (using animal slurry) can be often easily discriminated (Choi et al., 2003). The experimentation was carried out during 2014 (Maize) and 2015 (Wheat) cultivation cycles in the ZeoLIFE experimental field (Codigoro, Ferrara, Italy). Plants were sampled before the harvest, subdivided in stems and grains and analyzed by EA-IRMS in order to determine the δ15N and δ13C. Plants grown on NZ had significantly lower δ15N with respect to UA plants. Considering that the employed chemical fertilizers have a slight negative δ15N, it is highly possible that natural zeolites have adsorbed part of NH4 + ions formed after chemical fertilizers hydrolysis allowing plants to uptake higher amounts of N from this specific source, resulting in a lower tissues δ15N. On the other hand, both maize and wheat plants grown on CZ registered a significantly higher δ15N, approaching that of the pig slurry employed for enriching the zeolites, confirming that this material can constitute a N pool for plants at least for two cultivation cycles. The distinct agricultural practices seem to be reflected in the plant physiology, as recorded by the carbon discrimination factor (Δ13C), which generally increases in plots amended with natural zeolites indicating better water/nutrient conditions