Current crises focus our minds on the essentials in life, especially food security. The whole supply chain has been affected by sanctions on Russia and Belarus, which have disrupted a third of the world’s supply of potassium (K) fertilizers. For countries like Brazil (and other Latin American countries) which have no significant domestic source of K, this is especially serious given its essential role in agricultural production.

We have ongoing collaborations with the Escola Superior de Agricultura "Luiz de Queiroz" (ESALQ) in Piracicaba, which is part of the University of São Paulo, Brazil. As part of this, Dr Antonio Azevedo from ESALQ is visiting Newcastle on a CAPES Fellowship from January-June 2022. The primary reason for the visit is to investigate carbon capture in Brazilian soils, as a consequence of addition of volcanic rocks – a process we know works in Northumberland, where similar rocks occur in the Whin Sill. We now have the additional need to consider novel sources of K for crop nutrition, which we have both worked on through the Rochagem movement (http://www.cprm.gov.br/congressorochagem/).

Although naturally-occurring salts are the most common source of K for agriculture, a wide range of common silicate rocks has potential. Experience with their use in Brazil is growing, especially as a consequence of the development of federal regulations to govern their sale and use (IN5 Março 2016). There is a growing literature, from which other countries (including the UK) can learn. Weathering within the soil causes these silicate rocks to release the K that they contain, and biological activity (e.g. Baptista et al, 2022) is key to enabling this to happen on an appropriate timescale for crop growth.

The carbon cost of producing crushed rocks for agriculture is low; per tonne, it is about the same as that required to produce no more than 2 litres of milk. In addition to avoiding carbon costs involved in manufacture of chemical fertilizers, the carbon benefits include enhanced removal by soils of atmospheric CO2, through the process of ‘enhanced rock weathering’ which is being commercialised in the UK (e.g. Future Forest Company). Given the scale of agricultural production in Brazil, the combination of enhanced rock weathering and crop nutrition using silicate rocks produced locally offers possible contributions to solve problems of food security and climate change. More widely, this approach is now being discussed by the Intergovernmental Panel on Climate Change in their 6th Assessment Report (download Chapter 12).

David Manning (left) and Antonio Azevedo (right) examine an outcrop of the Whin Sill in Northumberland (2022).

ESALQ soil scientists visit the Sirius synchrotron; Antonio Azevedo 5th from left; David Manning far right (2019).‌‌