Greenhouse gas emissions under nanomaterial co-application with reduced fertiliser input

With the advent of synthetic nitrogen fertiliser, the proportion of reactive nitrogen (Nr) in terrestrial ecosystems has doubled. While this has enabled high crop productivity, it has also triggered mass environmental effects, with almost half of the applied fertiliser lost into air (in the form of N₂O or NH₃) as well as nutrient runoff and leaching of nitrates into water bodies. Nanomaterials present an opportunity to improve nutrient use efficiency of crops and minimise agricultural pollution via reducing losses. This study screened engineered nanomaterials, including zeolites and metal oxides, to assess their impact on greenhouse gas (CH₄, N₂O and CO₂) emissions when co-applied with NPK (nitrogen, phosphorus and potassium) fertiliser to grow lettuce (Lactuca sativa). The findings show that there are highly differential emissions from soils with nanomaterial co-application with reduced fertiliser application rates. One of the zeolites used, ZSM-5-15, when co-applied with a reduced dose (50% of RB209 nutrient management guide recommendation) of NPK fertiliser, increased N₂O emissions relative to reduced NPK fertiliser alone and negative controls. Another zeolite, BEA-19, had limited effect on either NH₃ or N₂O volatilization, but did reduce the concentration of ammonium in the leachate. Nitrate leaching gradually rose over the course of the 8-week experiment for full NPK fertiliser dose application, reduced NPK dose and negative control. This pattern was altered by BEA-19, triggering elevated nitrate leaching earlier in the experiment, peaking in week 1 compared to week 4 for other treatments. While nanomaterial treatment was able to increase lettuce biomass accumulation compared to full NPK and negative fertiliser treatments, understanding the impact of nanomaterials on N cycling has proven more complex. The mechanism for N loss from soils triggered by ZSM-5-15 application is unknown, potentially through impact on denitrifying enzymes. My work posits that the earlier release of nitrate from BEA-19 application is due to selective binding of the NPK to the nanomaterial surface. More data on nanomaterial endpoints is pending and may help elucidate the nature of this binding and nutrient release mechanisms.