Application of Nanomaterials in Precision Agriculture to Optimise Nitrogen Use Efficiency and Increase Global Food Security

Chadwick, Jessica ORCID: https://orcid.org/0000-0002-6133-4288 (2025). Application of Nanomaterials in Precision Agriculture to Optimise Nitrogen Use Efficiency and Increase Global Food Security. University of Birmingham. Ph.D.

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Abstract

Engineered nanomaterials (NM) are man-made nanoscale compounds, with at least one dimension between 1-100nm. Their utilisation presents a novel method to reduce the excessive use of synthetic fertiliser prevalent in industrial agriculture. The excess synthetic fertilisers are lost through the gaseous emission of N compounds, including N2O, NH3 and NOY, as well as through surface run-off and groundwater losses, increasing NO3- and NH4+ concentrations in waterways, impacting water quality. For NMs to be effective and sustainably used in agriculture there are several essential considerations that must be optimised: increased crop productivity and quality; positive effects on nutrient biogeochemical cycling, particularly N cycling to reduce emissions and run-off; and limiting impacts on soil biota including microbes and soil fauna, like earthworms.
The effects of NM exposure on seed germination were tested using seed priming experiments. NM effects were both species and NM dependent, although trends within “classes” of NMs were hard to predict, with constituent elements, concentration, agglomerate size, zeta potential and more sophisticated structure, like pore size, all impacting NM-plant interactions. NM application to soils in conjunction with reduced fertiliser application was used to determine NMs effects on plant growth and N cycling, using N2O gas sampling and N compound losses in leachate. Zeolite NMs can have very different effects on terrestrial N cycling, with the sophisticated structure of the NM likely the root cause of these differences. Zeolites of the same type, like BEA-19 and BEA-150, were used in different soils and had very different impacts on N emissions and losses, reflecting the importance of NM characteristics, on NM environmental effects. BEA-150 triggered elevated N2O emissions in the presence of microbes, while ZSM-5-15, another zeolite, decreased emissions in this soil type and increased them in another. This is indicative of the importance of soil abiotic factors, like soil moisture, clay and colloids, and soil microbial community composition on NM effect. Increased N2O emissions may be generated through a process of ion exchange, with ZSM-5-15’s extra-framework ion being exchanged for H+ ions in its pores, leading to an increase in NH4+ accessible for nitrifying microbes to act upon and increasing nitrification derived N2O. Wider effects of NMs on the soil environment were studied using earthworm reproduction assays. ZSM-5-15 also triggered sub-lethal effects on reproduction of the earthworm Eisenia fetida, reducing the number of unhatched cocoons at 25 mg L-1, a relatively low concentration. This may be through lower concentrations producing smaller NM agglomerates that are more able to pass through the worm epithelia and thus result in higher exposure at lower concentrations.
Ce0.75Zr0.25O2 NMs didn’t increase N2O emissions in the loam soil studied but did in the sandy loam, also increasing NO3- leachate concentration. Ce0.75Zr0.25O2 leaches Zr4+ ions into soil, transforming the NM into Ce0.9Zr0.1O2 and CeO2, as determined using X-ray near-edge absorption spectroscopy (XANES). Ce0.75Zr0.25O2 is able to translocate from lettuce roots to shoots, with the NM found in aboveground lettuce tissue after soil-based NM application. Zr metal and ZrCl4 were also found to be present in lettuce leaves, but whether these transformations occur in the soil before uptake and translocation or in lettuce shoots and leaves after uptake is uncertain. Other nano metal oxides used were TiO2 PVP and Co2.25Fe0.75O4 which were both applied in hydroponic medium. NM impact on N2O emissions from hydroponics was minimal, however K15NO3 stable isotope application showed that the majority of the N2O emissions were nitrification derived. This reflects the aeration of the rockwool substrate that the lettuce roots were grown in. TiO2 PVP and Co2.25Fe0.75O4 NMs may act on denitrifying microbes hence the minimal impact they have on total N2O emissions.
NM co-application with synthetic fertiliser was found to increase the risk of N losses to the environment, while NMs with nutrients as part of their physical structure may be able to limit these losses. Urea-doped amorphous calcium phosphate (U-ACP), a hydroxyapatite NM with both N and P within its structure, was able to reduce NOY emissions from soil. The lack of N2O and NH3 gas data however means that there are several N cycling endpoints that are missed, so whether U-ACP application reduces net N losses or shifts the balance of the soil N cycle is unknown. U-ACP increased lettuce production as compared to urea, with this mostly being derived from urea application triggering soil acidification and limiting lettuce growth. U-ACP application also increased the community of nitric oxide reductase (qNorB in particular) expressing soil bacteria, indicative of an increase in the soil microbial community active in denitrification.
Understanding NM impacts on N cycling is essential for a holistic view of fertilisation and for nano-enabled agriculture to truly increase sustainability while minimising the risk of regrettable substitutions. This thesis presents a first step towards achieving this holistic view.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):