Abstract
To investigate the effect of nitrification inhibitors (NIs) 3,4-dimethylpyrazole phosphate (DMPP) and 3-methylpyrazole 1,2,4-triazole (3MP + TZ), on N2O emissions and yield from a typical vegetable rotation in sub-tropical Australia we monitored soil N2O fluxes continuously over an entire year using an automated greenhouse gas measurement system. The temporal variation of N2O fluxes showed only low emissions over the vegetable cropping phases, but significantly higher emissions were observed post-harvest accounting for 50–70% of the annual emissions. NIs reduced N2O emissions by 20–60% over the vegetable cropping phases; however, this mitigation was offset by elevated N2O emissions from the NIs treatments over the post-harvest fallow period. Annual N2O emissions from the conventional fertiliser, the DMPP treatment, and the 3MP + TZ treatment were 1.3, 1.1 and 1.6 (sem = 0.2) kg-N ha−1 year−1, respectively. This study highlights that the use of NIs in vegetable systems can lead to elevated N2O emissions by storing N in the soil profile that is available to soil microbes during the decomposition of the vegetable residues. Hence the use of NIs in vegetable systems has to be treated carefully and fertiliser rates need to be adjusted to avoid an oversupply of N during the post-harvest phase.
Highlights
Agricultural activities are responsible for about 70% of anthropogenic nitrous oxide (N2O) emissions, a potent greenhouse gas with a global warming potential nearly 300 times that of CO2 and arguably the most important form of environmental nitrogen (N) pollution[1]
There was no significant effect of the nitrification inhibitors (NIs) on average NO3− concentrations compared to the CONV treatments, but NO3− concentrations were significantly reduced by the NIs following fertiliser applications in the green beans and lettuce cropping period (Fig. 3). This is the first study to report on the effect of NIs on N2O and CO2 emissions from an intensive vegetable crop rotation based on automated high frequency flux measurements
High frequency measurements are necessary to overcome the current uncertainty of N2O estimates from vegetable systems and to accurately quantify the inhibition effects of NIs on N2O emissions[12,13]
Summary
Agricultural activities are responsible for about 70% of anthropogenic nitrous oxide (N2O) emissions, a potent greenhouse gas with a global warming potential nearly 300 times that of CO2 and arguably the most important form of environmental nitrogen (N) pollution[1]. In addition to the high fertiliser N inputs vegetable crop residues typically have a low C/N ratio (8 to 17) and large amounts of N are incorporated into the soil after harvest (up to 450 kg N ha−1 yr−1)[4] Such residues are decomposed rapidly and release mineral N and readily available C into the soil, which combined with high O2 consumption rates during residue decomposition, can create anaerobic microsites in the soil and in turn enhance denitrification resulting in high long, lasting fluxes of CO2 and N2O following incorporation[5]. Most data on the effect of NIs on N2O emissions and productivity refer to forage or cereal systems or laboratory experiments and the efficacy of many NIs in vegetable production systems remains unknown Such data is urgently needed to identify management strategies that maximise the efficient use of fertiliser N while minimising environmental impacts from intensive vegetable production. The two main objectives of the study were: to investigate N2O emissions (including EFs) and vegetable yield from a typical vegetable rotation in response to different N fertiliser products; and to test the assumption that the use of NI will decrease N2O emissions
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