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Sensing soil processes for improved crop nitrogen bioavailability

Periodic Reporting for period 3 - SENSOILS (Sensing soil processes for improved crop nitrogen bioavailability)

Reporting period: 2018-09-01 to 2019-12-31

World agriculture and global food production relies heavily on the supply of water and fertilisers to maximise crop yield. However, current practise are now under increased scrutiny because of their impact on the environment and their potential vulnerability to climate change. The use soil resources and fertilisation must therefore be optimised, but studying biological processes in soil is difficult.
The recent development of transparent soils in my group gives great scope to unravel the processes involved in the reactive transport of nutrients in soil and their interaction with the soil biota. The broad aim of this project is to exploit and further develop the technology and understand the role of chemical and microbial process involved in nutrient movement at the micro-scale. We expect this research will not only shed new lights on what limit the efficient transfer of nutrients to crops, but also deliver fertiliser screens that more informative, improve the testing of new generation of fertilisers and promote the development of future fertilizers with less impact on the environment. New model soil systems could be used to better understand the spread of soil borne diseases, the bio-remediation of contaminated soils and the mechanisms underlying soil biodiversity and activity.
All four work packages have started with key progress being made in the fabrication of core-shell structure that allows functional fluoropolymers to be attached to FEP particles, the development of a model system to study microbial activity in the rhizosphere, and the development of new approaches to model biophysical processes in the rhizosphere.
(WP1) – New generation of smart soil particles
The objective of this work package is to develop new types of artificial transparent soils for both the measurement of biological activity and the measurement of nutrient concentration in the rhizosphere. In order to achieve this objective, we have adopted a core-shell strategy for the design of soil particles. The core of the particle is composed of a material chosen for its low refractive index and transparency. The core material must also be amendable to attachment and coating by the active polymer so that a thin shell is built around the core particle. In order to achieve this objective, and as fluoropolymers are well known for their transparency, we chose to use a copolymer based on tetrafluoroethylene and hexafluoropropylene (called Fluorinated Ethylene Propylene, FEP) instead of Nafion® as core material for the particles. Actually, FEP is not as transparent as Nafion®, but it is of lower cost, can be easily sourced from commercial suppliers, has a refractive index closer to water and its chemistry is more amendable to interactions with other fluorinated polymers. The shell must also be made of a low refractive index polymer, transparent, but it must incorporate numerous functions such as ion exchange, chemical sensing, and possible adhesion.
A number of key milestones have been reached toward the making of sensing soil particles. These include porotocols for the making of FEP cores. FEP is quite different from Nafion because the temperature at which it becomes more ductile is lower than Nafion. Obtaining suitable particle size with FEP particles is therefore much harder than with Nafion. We have successfully attach various polymer and co-polymer on the surface of FEP membranes and particles. FEP has been developed originally as a non-sticky inert material and to date this is the first time such coatings have been achieved. The coating was made of novel terpolymers based on 1,1,1,3,3,3-hexafluoropropyl a-fluoro acrylate (FAHFiP), 2-(trifluoromethyl) acrylic acid (MAF) and fluorescein 2-(trifluoromethyl) acrylate (MAF-fluorrescein).
The ability to attach fluorinated terpolymers on FEP core particles was also followed by several breakthroughs in the synthesis of such fluorinated copolymers which structure and composition are being tailored to obtain suitable physical and chemical properties. Our terpolymers are based on either 2,2,2-trifluoroethyl α-fluoroacrylate (FATRIFE) or 1,1,1,3,3,3-hexafluoroisopropyl α-fluoroacrylate (FAHFiP) backbones to which various other monomers are introduced for control of hydrophilic behaviour, ion exchange, fluorescent marking, sensing, etc. Original block copolymers that display a sequence adhesive to FEP and the other one hydrophilic have been obtained via RAFT sequenced copolymerization. Control of hydrophilic behaviour and ion exchange of the co-polymers are achieved through incorporation of 2-(triuoromethyl)acrylic acid (MAF) groups in the terpolymers. To evidence such a trend, we first focused on the synthesis of poly(MAF-co-FATRIFE) copolymers both of them inducing complementary properties. These copolymers showed that increasing the MAF concentration in copolymers also induced a reduction of the contact angle of polymer coatings and thus a hydrophilicity (a first article was published in Polym. Chem. Banerjee et al. 2017). We have also successfully included Fluorescein in our co-polymers and this demonstrates the possibility of obtaining constitutive fluorescence. The fluorescein coatings were successfully detected by various microscopes and plant growth was successfully tested on t
"Four main areas of the project have significantly advanced the field and moved beyond the state.
First, the development of core shell structure technologies to make sensing soil particles or ""Sensing soils”. These will have a broad range of application, for example in scientific research, breeding and development of fertiliser. It has required significant advancement in polymer sciences, and the techniques could be used in other areas of science and technology.
Our work is greatly contributing to the field of soil microscopy. We have developed a series of approaches that allow live observation of soil microbes. We fabricated new fluidics systems for soil control of soil conditions under a microscope.
Computational modelling work for simulation of root development in soil is extremely promising. We anticipate we will be possible to make simulation of entire roots at cellular resolutions while at the same time model the soil at the particle level. The model and algorithms are being implemented in DualSPHysics, an open source community led simulation tool.
Work focused on understanding factors affecting microbial activity in the rhizosphere is, and is just starting to benefit from the technological development from the project. In particular, we expect to be able to quantify accurately the mobility coefficient of soil microbes surrounding plant roots and predict what contributes to maintenance of certain microbes at the tip of the root.