Abstract
The use of synthetic N fertilizers has grown exponentially over the last century, with severe environmental consequences. Most of the reactive N will ultimately be removed by denitrification, but estimates of denitrification are highly uncertain due to methodical constraints of existing methods. Here we present a novel, mobile isotope ratio mass spectrometer system (Field-IRMS) for in-situ quantification of N2 and N2O fluxes from fertilized cropping systems. The system was tested in a sugarcane field continuously monitoring N2 and N2O fluxes for 7 days following fertilization using a fully automated measuring cycle. The detection limit of the Field-IRMS proved to be highly sensitive for N2 (54 g ha−1 day−1) and N2O (0.25 g ha−1 day−1) emissions. The main product of denitrification was N2 with total denitrification losses of up to 1.3 kg N ha−1 day−1. These losses demonstrate sugarcane systems in Australia are a hotspot for denitrification where high emissions of N2O and N2 can be expected. The new Field-IRMS allows for the direct and highly sensitive detection of N2 and N2O fluxes in real time at a high temporal resolution, which will help to improve our quantitative understanding of denitrification in fertilized cropping systems.
Highlights
We present a novel, mobile isotope ratio mass spectrometer system (Field-Isotope Ratio Mass Spectrometry (IRMS)) for in-situ quantification of N2 and N2O fluxes from fertilized cropping systems
The new Field-IRMS was developed by the Queensland University of Technology (QUT) in collaboration with Sercon (Sercon, Crewe, UK) and is housed in an air-conditioned trailer which can be transported to the desired field location
To test the performance of the novel system under field conditions we investigated the effect of two different fertilizer rates on the magnitude and the partitioning of N2 and N2O denitrification losses from a sugarcane cropping system in subtropical Australia (24°57′53′′S, 152°20′0′′E)
Summary
We present a novel, mobile isotope ratio mass spectrometer system (Field-IRMS) for in-situ quantification of N2 and N2O fluxes from fertilized cropping systems. Under field conditions it is unlikely to achieve homogeneity of the added 15N tracer with the soil NO3− pool, but it has been shown that accurate estimates of gaseous N losses can be made without uniform distribution of 15N in the soil when large amounts of highly enriched N fertilizer are applied[9]. The 15N gas flux method is most applicable for fertilized cropping systems where large amounts of enriched N fertilizer with water can be applied and high fluxes of N2 and N2O can be expected Another constraint for field measurements of denitrification is the high temporal (diurnal, daily and seasonal) variability of N gas emissions that compromise flux estimates if not carried out with an adequate frequency. Such instrumentation has not been available for both N2 and N2O measurements
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