Breaking ground: Professor makes “rocks for crops” reality in Cameroon

Slope of Mount Cameroon. Photo by Jean-Baptiste Dodane

In the early 2000s, Jean Pierre Nguetnkam, a full professor in the Department of Earth Sciences at the University of Ngaoundéré, Cameroon, was inspired to start a research program on soil remineralization involving the use of locally sourced natural geologic materials to restore and enrich agricultural soils. His inspiration came chiefly from conversations with local farmers. 

“I became interested in soil remineralization through discussions with farmers who were complaining about the steady decrease of their soil fertility, which negatively impacted their harvests and yields, even with the use of chemical fertilizers,” Nguetnkam told RTE. 

Professor Jean Pierre Nguetnkam

Dr. Nguetnkam looked into the literature and was particularly influenced by Peter van Straaten’s 2002 book “Rocks for Crops: Agrominerals of Sub-Saharan Africa.” By 2009, professor Nguetnkam had formed a research team and was performing pioneering experiments on soil remineralization with several types of rock dust, biochar (charcoal produced by combusting agricultural wastes in a low-oxygen environment), and other natural soil additives. Over the past several years, Nguetnkam has supervised or co-supervised over twenty master’s degree students and six PhD students whose research focused on soil remineralization. The participation of other professors in “rocks for crops” research has also grown. Nguetnkam reports that roughly ten senior researchers are involved in this work, four from the University of Ngaoundéré and the rest from other Universities throughout Cameroon. 

While the adoption of using rock dust for soil remineralization by smallholder farmers has been slow (due mainly to the lack of availability), the Cameroon remineralization research team has shown its great potential. Several studies show that rock dust soil amendments can improve soil properties, increase crop yields, and reduce dependence on environmentally hazardous synthetic fertilizers. Still, Professor Nguetnkam told RTE that he is not aware of any companies using or selling rock powder for agricultural purposes; he explained, “This [soil remineralization with rock dust] is still at the level of research, although the results are very promising.”  

Promising Experimental Results

After performing numerous detailed scientific tests on the effectiveness of different rock dusts for agricultural use, Nguetnkam and his team of students and colleagues report four central findings: 

  1. Silicate rocks (i.e., rocks containing abundant oxygen-bonded silicon, aluminum, sodium, potassium, calcium, magnesium, and iron) that have been ground into powder make excellent soil remineralizers. 
  2. Several key chemical soil properties showed measurable improvements after silicate rock dust application. For example, soil pH improved, as did nutrient retention and cycling.
  3. Silicate rock dust applications increased the concentrations of important nutrients in crops, including essential minerals and trace nutrient elements.  
  4. Silicate rock dust increased crop yields and improved plant resistance to diseases and insect pests.
Mt. Cameroon, a potential source of volcanic silicate rock dust for soil remineralization (Wikimedia Commons, credit Obenrodney60).

As an example of Dr. Nguetnkam’s research team’s work, in 2019, master’s student Daw Henri performed tests assessing the fertilizing effect of a metamorphic rock called gneiss on soils from Djalingo in north Cameroon. The rock powder used for these experiments was waste material from a mining company’s rock-crushing facility (the Mouchouka company). The gneiss rock dust was applied to pots filled with degraded soil (Ultisol) from Djalingo. Four months after the rock dust treatment, measurements of soil chemical properties showed improved (i.e., increased) soil pH and cation exchange capacity (the soil’s ability to retain the key nutrient elements calcium, magnesium, and potassium). The rock dust was found to be an excellent source of the essential nutrient potassium (due to high levels of the minerals potassium feldspar and biotite mica) and increased plant-available phosphorus. 

In another study, Dr. Nguetnkam’s master’s student Djafarou applied phonolite (a volcanic rock) powder to highly weathered, low fertility soils (Oxisols) from the Ngaoundéré region. Six months after the addition of phonolite rock dust (applied in pots), both the soil pH and nutrient levels (specifically potassium) improved significantly.  

Acidic and nutrient-depleted red lateritic soils (Oxisols) in Cameroon (Wikimedia Commons, credit EzekielFokam). 

Professor Nguetnkam’s research group has also investigated the effectiveness of the common volcanic rock type basalt for soil remineralization. Master’s student Clarisse Djao Mein’da, under the supervision of Dr. Nguetnkam, applied basalt rock dust to the soil in pots containing common bean plants (Phaseolus vulgaris L.). The rock material was added at different growth stages: seeding, sprouting, and flowering. The starting soil material was acidic and depleted in mineral nutrients. Results from the study showed that basaltic rock dust improved growth and harvest output relative to untreated control pots. Plants grown in soils treated with basalt show increases in height of 51% and a 100% increase in number of leaves relative to controls. The bean yield for basalt-treated plants was around 76%, and there was a 16% increase in protein and a 59% increase in calcium in the harvested beans relative to untreated plants. These experiments also showed that basalt treatment improved the bean plant nitrogen fixation efficiency (nodule growth) relative to controls. It was found that the ideal timing for treatment was during the seedling stage of plant growth. The study recommended that local farmers in the Adamaoua region (north-central Cameroon) apply local basalt rock powders to their bean crops to increase harvest yields and nutrient density.

In addition to these key findings, the widespread use of natural, locally sourced rock dusts provides a natural, sustainable alternative to synthetic fertilizers that are costly and may cause environmental damage (e.g., eutrophication of lakes and ponds) when used extensively. 

The Future of Rock Dust Remineralization in Cameroon

Professor Nguetnkam indicates that his team’s future research in soil remineralization will focus on how rock grain size influences the measured agricultural benefits, and they will also expand research into the effectiveness of soil amendment mixtures that combine rock dust with other organic materials such as biochar and manures. Scaling up the use of agromineral fertilizers, which will require external funding, is another theme that Dr. Nguetnkam emphasizes. For example, in a recent interview with RTE, he said that:

“Since farmers are already adopting the little quantities of agromineral fertilizers from our research, it could be assumed that, if really available in large quantities, wide adoption could be considered a foregone success. However, large scale production of agromineral fertilizers would involve some expensive equipment and infrastructure, which are not financially within our reach, and thus call for external funding.”

Efforts have been made to collaborate with government agencies to help scale up and develop public policy around using locally sourced soil remineralizers; however, these efforts have yet to reach their full potential. Professor Nguetnkam hopes that government officials will embrace the use of agrominerals, including silicate rock dust and biochar, in the future. The science speaks for itself. Dr. Nguetnkam, his students, and his colleagues’ meticulous work has contributed to global efforts to demonstrate the vast potential of silicate rock dust and biochar as nature-based solutions to soil degradation and infertility. Scaling up the use of rocks for crops promises not only to decrease reliance on costly and environmentally damaging synthetic fertilizers, but also has the potential to increase harvest yields, thus addressing both economic and food security issues in Cameroon and near-by countries in sub-Saharan Africa.

James Jerden is an environmental scientist and science writer focused on researching and promoting sustainable solutions to urgent environmental problems. He holds a Ph.D. in geochemistry from Virginia Tech and a Master’s degree in geology from Boston College. Over the past 20 years, James has worked as a research geochemist and science educator. He joined Remineralize the Earth because of their effective advocacy, research, and partnership projects that support sustainable solutions to urgent environmental issues such as soil degradation (food security), water pollution from chemical fertilizers (water security), deforestation, and climate change. As a science writer for RTE, his goal is to bring the science and promise of soil remineralization to a broad, non-technical audience. When not writing, he can be found at his drum set.

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