Novel geological sources of crop nutrients for tropical agricultural systems in rift valleys

Located on the East African Rift, Malawi hosts a range of nepheline syenites and related rocks that have potential to act as sources of crop nutrients. The country is one of the poorest in the world, and at present depends on imports of chemical fertilizers which are reduced in supply and greatly increased in price because of the war in Ukraine. It is known that nepheline syenite is an effective source of K for crop growth, and recent work with crushed rock in Brazil has shown the value of a wide range of silicate rocks as alternatives to chemical fertilizers in farming systems based on deeply weathered tropical soils. The purpose of this PhD is to carry out a thorough investigation of the potential of rocks to be used in the production of key crops in Malawi, working in collaboration with the Geological Survey of Malawi and local universities. The knowledge gained will be extended to other countries that can benefit from this approach, including the UK.


First, an inventory of candidate rocks will be drawn up, using local geological knowledge from partners in Malawi (Geological Survey of Malawi; their Chief Geologist Dr Annock Chiwona completed his PhD on a related topic in Newcastle in 2019). The inventory requires whole rock analysis and determination of the minerals (and their compositions) within the rocks, as the ability of a rock to release nutrients depends on mineral dissolution rates. Secondly, to understand processes, leaching tests will be carried out in the laboratory in Newcastle to establish nutrient release rates. Although that information ideally is needed first, the timing of growing seasons requires that crop trials under local conditions will be undertaken. The crop growth trials will be carried out under the supervision of Dr Patson Nalivata of Lilongwe University of Agricultural and Natural Resources (LUANAR) to ensure agricultural relevance. Offtake of K and other nutrients will be measured, together with soil nutrient contents, so mass balances can be determined, and field release rates calculated for the individual rocks used. Additionally, soil carbon (inorganic and organic) will be measured to assess the CO2 removal potential of the crushed rocks. The trials will be designed in such a way that full statistical analysis will be carried out.

Project Timeline

Year 1

Development of the inventory of candidate rocks, compiling existing XRF/ICP analyses and securing new analyses to fill gaps; preparation of polished thin sections for micro-analysis; initial training on geochemical analytical methods (e.g. electron beam analysis). Design of first round of leaching tests, pot trials (Newcastle) to select rock types for crop trials. Substantial field work (including rock collection) in Malawi.

Year 2

Completion of rock leaching experiments in Newcastle, with completion of XRF/ICP analysis at BGS, and initial round of petrographic analysis (BGS). Integration of pot trial results with leaching results to plan field trials for Year 3, and to generate first research paper for submission.

Year 3

Field work in Malawi to set up and observe field trial (December sowing). Oversight of harvest and analysis of soil and crop products using local laboratories, collecting data to facilitate modelling of yields as a function of rock type and application rate – to give second publication.

Year 3.5

Final writing up period in Newcastle, producing thesis and additional papers that extend the work to other systems and locations.

& Skills

Truly inter- and multi-disciplinary training, with a combination of research-level use of geochemical and micro-analytical techniques, field crop trials and statistical analysis, assessing the biogeochemistry of crops from the point of view of the cations they require and the potential geological sources of these. Much of the training will involve engagement with experts in different disciplines at a high level and local stakeholders (e.g. farmers, landowners, exploration companies, quarry owners). The engagement with stakeholders will provide them with opportunities to influence resource management practices and policy specifically in Malawi but also with implications for other countries with similar challenges.

References & further reading

1) Manning, D. A. C. (2022) Mineral stabilities in soils: how minerals can feed the world and mitigate climate change. George Brown Lecture, Clay Minerals, https://doi:10.1180/clm.2022.17
2) Manning, D. A. C., Theodoro, S. H. (2020) Enabling food security through use of local rocks and minerals. The Extractive Industries and Society, 7, 480-487. https://doi.org/10.1016/j.exis.2018.11.002
3) Chiwona, A. G., Cortes, J. A., Gaulton, R. G., Manning, D. A. C. (2020) Petrology and geochemistry of selected nepheline syenites from Malawi and their potential as potash sources. Journal of African Earth Sciences, 164, 103769. https://doi.org/10.1016/j.jafrearsci.2020.103769
4) Broom-Fendley, S., Elliott, H. A., Beard, C.D., Wall, F., Armitage, P. E., Brady, A. E., Deady, E., Dawes, W. (2021) Enrichment of heavy REE and Th in carbonatite-derived fenite breccia. Geological Magazine, 158, 2025 – 2041. https://doi.org/10.1017/S0016756821000601
5) Beard, C. D., Goodenough, K. M., Borst, A. M., Wall, F., Siegfried, P. R., Deady, E. A., Claudia Pohl, C., Hutchison, W., Finch, A. A., Walter, B. F., Elliott, H. A. L., Brauch, K. (2022) Alkaline-Silicate REE-HFSE Systems. Economic Geology doi: https://doi.org/10.5382/econgeo.4956
6) Goodenough, K. M., Deady, E. A., Beard, C. D., Broom-Fendley, S., Elliott, H. A., van den Berg, F., Öztürk, H. (2021). Carbonatites and alkaline igneous rocks in post-collisional settings: storehouses of rare earth elements. Journal of Earth Science, 32, 1332–58. https://doi.org/10.1007/s12583-021-1500-5
7) Milheiras SG, Sallu SM, Marshall AR, Shirima DD, Kioko EN, Loveridge R, Moore E, Olivier P, The YA, Rushton S and Pfeifer M (2022) A Framework to Assess Forest-Agricultural Landscape Management for Socioecological Well-Being Outcomes. Front. For. Glob. Change 5:709971. https://doi.org/10.3389/ffgc.2022.709971
8) Moore, E., Howson, P., Grainger, M. The, YA and Pfeifer, Ml. The role of participatory scenarios in ecological restoration: a systematic map protocol. Environ Evid 11, 23 (2022). https://doi.org/10.1186/s13750-022-00276-w

Apply Now