Application of isotopic labels optimised for large scale plot experiments

Abstract Isotopic tracer methods using 15 N or other isotopes provide insights into the sources and underlying transformations leading to 2 O emissions from agricultural soils. However, homogeneous labelling of naturally structured soil in field is challenging since macropore flow must be avoided while application performed a limited timeframe. Therefore, we tested infiltration pattern several consequently developed drip (DA) for larger scales individual dropper bottles. We proof concept test, followed by an evaluation experiment in-situ with manual sprinkler as control at undisturbed grassland site NH 4 NO 3 (80 kg ha -1 , 10 at.%, mm precipitation equiv.). N-NH + N-NO - recovery rates corresponding correlation coefficients were calculated examine horizontal vertical homogeneity. The test showed negative effect very dry topsoil on infiltration. DA achieved significantly than led more label distribution. For DA, variation smaller sprinklers most depths, yet both especially decreased vertically. Besides optimised distribution, method offers high flexibility patterns offering reproducibility, feasibility reasonable speed also sites plot scale. Moreover, causes no change structure diffusivity. Thus, was found suitable sites.