Results from Flux field research: harvests increase over 70% on Kenya farms after spreading rock powder

The impact of carbon removal on climate change is intangible. But extra money, earned from a more productive farm with richer soil, is impact that you can put in your pocket. When farmers earn more because of enhanced rock weathering activities they become carbon removal partners, and this opens more fields for carbon drawdown on a basis of trust. 

Rural livelihoods are essential for Flux’s work. It is not so much a “co-benefit” as a prerequisite for community relationships and through it, growth. 

That’s why the science team tries to quantify this impact, just like we measure the impact of carbon sequestration. We found that spreading our silicate rock powder, which is an inorganic fertilizer, on fields improved harvests and added more than $300 per hectare in terms of the value of harvested crops.

The impact on farms

In 2024 Flux conducted tests in 31 smallholder farms in Kisumu County, Kenya. With farmers’ consent, the science team spread rock powder in one portion of the farms shortly after planting. The impact on crop growth was measured months later. 

The findings, published in a November 2024 scientific white paper, show “significant agronomic benefits.” So significant that we were surprised. There was a 71.2% average increase in agricultural yield in the plots that had rock powder spread on them, compared to adjacent plots where the farmers went about their normal farming practices. The result was influenced by a few outliers where productivity jumped 200% or higher. So we also used a different measure: aggregate yield change. The average rise in yield was still 47.5% across the 31 farms. 

The aerial photo below captures the impact. On the right half of the field is the “control:” the section left unchanged. On the left is the “experiment:” the section dusted with magnesium- and calcium-rich rock powder. The dense green is the leaves of maize plants growing 7 weeks after planting and fertilisation.

The chart below shows yield results in farms spread across two geographical clusters in Kisumu County. Many harvests increased by over 30% after applying the rock-based fertiliser, in line with the aggregate yield change result.

The benefits for farmers

How do farmers benefit? Calculating this was straightforward, after the yield results were finalised. 

• The average weight in harvested maize from the fertilised plots was 3,075 kilograms per hectare. 
• The “control” plots without silicate rock fertiliser yielded an average 2,085kg per hectare, reflecting fewer and/or smaller maize plants. 
• The market price of maize at the time was 43 Kenya Shillings per kilogram. 
• The average 989kg of extra maize per hectare would create $326 per hectare, per harvest.  

Some smallholder farms are more than a hectare, and some less. Harvesting more than once a year will influence how much farmers can gain. Another key variable — which the science team will explore — is the influence of different soil types and climatic conditions in other regions of Kenya and sub-Saharan Africa. 

The clear conclusion, however, is that a typical smallholder farmer in one county of Kenya could expect to make a few hundred extra dollars per year by using a enhanced rock weathering-based fertiliser product that we give away for free. That income makes a difference for smallholders farmers: it can pay for extra food for a family, school tuition, farm equipment, or even chemical fertilisers that boost farm yields even higher.  

At scale, this also makes a difference for food security in sub-Saharan Africa. 

Meanwhile the rock dust spread on those fields is reacting with the carbonic acid in rain- and groundwater and removing carbon dioxide from the atmosphere. 

This is the kind of impact that Flux was set up to achieve. It’s not about one benefit with co-benefits. It’s about multiple benefits — some tangible, some less so — for people and planet, all at once, with each reinforcing the other and delivering impact at scale. 

Read more about this research by Fatima Haque, Vincent Clementi, Benjamin Moller, and others in our science team: Yield increases for smallholder farmers in Sub-Saharan African via enhanced rock weathering: preliminary results from a smallholder field trial in Kisumu County, Kenya.