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Novel Release-on-demand micronutrient fertilisers for crops

Periodic Reporting for period 1 - MicroFert (Novel Release-on-demand micronutrient fertilisers for crops)

Reporting period: 2015-08-01 to 2017-07-31

In many important agricultural crops successful fertilisation with micronutrients can lead to substantial increases in resistance to diseases, significant increases in the marketable yield, and improved nutritional quality of food and feed. However, the plant availability of supplied micronutrient fertilisers is in many cases too low due to the high reactivity of fertilisers under unfavourable soil conditions. New and more efficient micronutrient fertilisers may therefore make a substantial contribution to improving production systems for important agricultural crops
Recently novel concepts for designing ‘slow release’ or ‘controlled release’ fertilisers have been adopted which try to extend their time of availability in the soil in different ways. This project introduces the release-on-demand concept in which the plants themselves trigger the release of nutrients from nanoparticles at the time in their growth cycle that they need them. Layered Double Hydroxides (LDHs) used in development of drug delivery systems are currently being developed in the host institution and are seen as interesting candidates for the controlled release of nutrients including trace nutrients in the formulation of new fertilisers. LDHs consist of alternating layers of positively charged metal hydroxides and interlayers of charge compensating anions so they can include both divalent and trivalent metal cations, e.g. Mg2+, Fe3+, Al3+, Cu2+, Zn2+, Mn2+ and many different interlayer anions, e.g. carbonate, nitrate, sulphate, phosphate, selenate and molybdate. The nutrient release is expected to be dependent on rhizosphere acidification occurring via root excretion of protons, low molecular organic acids and/or CO2. In addition, root derived carboxylates may complex metal cations and facilitate their release from the LDH. Moreover, there is a strong interest in their patenting and utilisation, ensuring a high likelihood for their future commercialisation should the results of this study be promising.
The overall objective of this MC project is to evaluate the potential of synthesised LDHs as release-on-demand micronutrient fertilisers, mainly focusing on Zn, Mn and Cu, but also their interactions with N under a range of soil conditions and growing conditions. The experiments conducted cover both highly controlled stability and nutrient release in solution and delivery to several important plant species under alternating soil conditions.
A successful work has been performed during the 20 months project, which has followed the plan initially proposed. Slight modifications have been introduced due to the results obtained along the project progress.
The LDHs containing Zn, Mn, and Cu have been successfully synthetized and chemically characterized. Studies conducted on their solubility in different extracts and their nutrient release in aqueous solution at different pH and time and in soils have demonstrated the pH-dependant release of the LDHs which dissolves at the pH of rhizophere (about 5.5). The results obtained clearly highlight that the LDHs have a strong potential to be used as micronutrient fertilizers. The relationship between their effectiveness and their chemical behavior has been demonstrated.
Furthermore, the combination of the synthetised materials in macronutrient granules has shown to be the most promising use of this new type of fertilisers.
Exploitation and Dissemination
The results from the work developed over the MC have been already disseminated in a conference (Nutriplanta 2016, Murcia, Spain), while they will be presented in two more conferences which will be held during the summer (IPNC 2017, Copenhagen, Denmark, and ICC2017, Granada, Spain):
López-Rayo, S., Imran, A., Hansen, H.C.B. Schjoerring, J.K. Magid, J. Layered double hydroxides: a new concept for zinc fertilizers. Nutriplanta: XVI Simposio Hispano-Luso de Nutrición Mineral de las Plantas 26th – 29th September 2016, Murcia, Spain.
López-Rayo, S., Schjoerring, J.K. Hansen, H.C.B. Magid, J. Layered double hydroxides: a novel use as micronutrient fertilizer. International Clay Conference 17th – 21st July 2017, Granada, Spain.
Sandra López-Rayo, Hans C. B. Hansen, Jan K. Schjoerring, Jakob Magid. Novel control-release fertilizers based on layered double hydroxides for manganese nutrition. International Plant Nutrition Colloquium: Manganese satellite meeting 20th August 2017, Copenhagen, Denmark.
Sandra López-Rayo, Hans C. B. Hansen, Jan K. Schjoerring, Jakob Magid. Zinc doped layered double hydroxides: a new source for zinc fertilization. International Plant Nutrition Colloquium 21st – 24th August 2017, Copenhagen, Denmark.
Two patent processes haves been initiated in Denmark for patenting the preparation and use of the LDHs.
The manuscripts´ publication is expected to be completed over the next year, since data are still being processing. A first manuscript including the Zn released from the LDHs and the plant uptake has been recently submitted to the journal Plant and Soil.

Due to the patent processes in which we are involved, the dissemination activities have been limited during the MC period. However, the results obtained over the MC have been really successful and we will disseminate them as soon as this can do. A few activities have been done. Publication in Agronomical magazines will be done to access farmers and stakeholders. Other web services will be used for dissemination.
Despite the fact that LDHs have properties similar to cationic clays they had never been evaluated for use as micronutrient fertilisers. Their versatility in modifying the layer cations and the interlayer anion gives to these compounds a high potential value as fertilisers providing several essential nutrients. Their stability at pH over 7 makes possible their introduction as a novel category of fertilisers: the release-on-demand fertilisers. This principle will improve costs and avoid the need for repeated applications, since only one application will be necessary to cover the nutrient requirements over the plant crop cycle.
The further development of DGT combined with LA-ICP-MS for metal micronutrients in 2D is new and the host group is the best environment for this taking into account their knowledge in this technique. The use of isotopic labelling as well as the determination of the composition of organic acids in plant tissues and root exudates in plant experiments are both advanced techniques to reveal the effect of LDH as nutrient sources. The collaborations with the Autonomous University of Madrid and Timac Agro (and the University of Navarra) had increased the researcher´s expertise in plant nutrition techniques and have opened a door for further collaboration opportunities. In fact, the researcher has been incorporated at the Autonomous University of Madrid as Assistant professor where she will continue her researcher and teaching career. This fact demonstrate the highly impact of the MC fellowship in the researcher career development.
This project has demonstrated to be extremely timely and highly relevant to both end-users, stakeholders, i.e farmers and fertiliser manufacturers, and to the European Community for which sustainable agriculture is an important issue. The results obtained provide new information to support improving the efficacy of these fertilisers and to enable their patenting and introduction to the market.
Figure 1. Zn, Cu, and Mn release over time from LDHs incubated at different pH levels for up to 28 d