Engineers Without Borders is Addressing Food Security in Tanzania

David Paul and Pupils of Chagu Primary School fetching water from the lake with crocodiles.

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David Paul Blessing, current president of Engineers Without Borders-Tanzania (EWB-Tanzania), sat in his hotel room in Nguruka township after a long day of work. He and his team were on-site helping to develop safe drinking water sources and sanitation facilities for residents of the Kigoma Region in western Tanzania. He was musing over a recent conversation in which Jackson Buzingo, Executive Director of the One More Salary organization, told of his recent training in nature-based, regenerative agricultural methods and how it allowed him to help small-scale Tanzanian farmers improve their farming techniques. 

The inspirational conversation triggered a new outlook for David Paul. He asked himself how EWB could contribute to the spread of sustainable agriculture in Tanzania. How could he and his colleagues help address issues of food insecurity and poverty among small-scale farmers? He was particularly intrigued with the idea of helping locals adopt sustainable and environmentally restorative farming practices that improve crop yield and produce nutrient-dense foods. As he had discussed with Mr. Buzingo, one of the significant problems for smallholder food producers in Tanzania is the lack of access to effective fertilizers. Many large-scale farms rely on imported nitrogen-phosphorus-potassium (NPK) amendments that are not only prohibitively expensive for most small-scale farmers but also degrade soils when used excessively. 

As David Paul thought through the issues, he wondered if there was a way to provide farmers with low-cost, nature-based fertilizers that are locally sourced and more environmentally friendly than synthetic amendments. His musing led him to wonder how nature creates and sustains intrinsically fertile soils that do not require fertilization. He asked himself, what natural processes sustain the rich and fertile soils in the northern highlands near Kilimanjaro and the southern highlands of the Rungwe district near Mbeya? And why do the soils of the central plateau near Tabora have low natural fertility? What was the source of soil nutrients in the fertile regions?

David Paul instinctively knew that the answer to his questions must have to do with the types of rocks from which the soils had formed. The fertile highland soils were formed from alkaline volcanic rocks deposited in the recent geologic past. In contrast, the less fertile soils of the central plateau were formed from geologically ancient granitic rocks. The minerals in the volcanic rocks provided a natural wealth of plant nutrients leading to well-developed, organic-rich soils. The soils formed over the ancient granitic rocks of the central plateau have lower natural nutrient levels and are largely devoid of accumulated organic matter. 

This realization led David Paul to consider the possibility of using rock material collected from the nutrient-rich volcanic regions to naturally fertilize or remineralize less fertile soils in other regions. He realized that this local source of natural, rock-based fertilizer could form the basis of a new project to help smallholder farmers enrich their soils and enhance crop yields without expensive, synthetic fertilizers. After sketching out the concept of this new project, David Paul dove into the scientific literature on soil remineralization. He began collaborating with long-time experts in the field, such as Joanna Campe, Founder and Executive Director of Remineralize the Earth. 

By following up on his inspiration, David Paul and colleagues at EWB-Tanzania have developed a plan for how local rock-based agromineral mixtures can be used to remineralize depleted soils and address the urgent problems facing Tanzanian Agriculture.

The Challenges Facing Tanzanian Agriculture

Local fertilizer self-sufficiency (or independence) is recognized as a critical aspect of food security, especially in light of how global pandemics, wars, and political upheaval can disrupt supply chains. As professors Ward Chesworth, Peter van Straaten, and Johnson Semoka put it:   

“A country that does not control the means to maintain the fertility of its soil is essentially dependent on foreign imports of fertilizer. The legitimate hope that people have to secure their food supply cannot ultimately be achieved in such a situation. In other words food security depends to a substantial degree on fertilizer self-sufficiency.” 

The increasing cost of imported fertilizer severely limits access to synthetic nitrogen, phosphorus, and potassium (NPK) amendments, limiting crop yields, causing financial insecurity among smallholder farmers, and increasing food insecurity among subsistence farmers. Tanzania imports around 90% of the fertilizer used in the country, and it is estimated that over 95% of small-scale farmers in Tanzania have very limited to no access to synthetic fertilizers. Fertilizer prices have doubled due to the Russia-Ukraine conflict. This will limit crop yields throughout the country, exacerbating already dire food security issues. The fertilizer supply crisis underscores the importance of fertilizer independence, which is why David Paul’s vision for a locally sourced, Tanzanian agromineral product is so important and timely. 

Another major challenge is that Tanzanian agriculture is dominated by subsistence farming. As well as being a significant contributor to poverty, Tanzanian subsistence agriculture is highly susceptible to the effects of climate change, such as prolonged droughts. This is further exacerbated by the escalating cost and reliance on imported fertilizers. Even for those larger-scale farmers who can afford synthetic fertilizers, their soil continues to lose fertility because of the lack of micronutrients in the NPK amendments, along with other harmful effects.  

The EWB-Tanzania agromineral project will address the central “lack of resources” issue by providing farmers with locally sourced soil amendments containing all major micronutrients needed to remineralize depleted soils. If successful, the project would also contribute to the adoption of regenerative farming methods with long-term positive consequences.

Soil Remineralization

Soil remineralization is a nature-based process involving the natural dissolution or weathering of nutrient-bearing rock dust that has been added to agricultural soil. Different rock types contain different minerals, each with a unique suite of elements. As the rock’s primary minerals dissolve, secondary minerals (such as clays) form, and nutrient elements are released into the water-based soil solution that partially fills pore spaces in the soil. Once dissolved in the soil solution, the elements react to form ions such as potassium (K⁺), calcium (Ca²⁺), and phosphate (HPO₄^2-) that enhance the growth potential of beneficial microorganisms and serve as essential nutrients for plants. 

There are 17 essential macro and micro or trace nutrients needed for the growth of healthy, nutrient-dense food crops.

All of these nutrients are also essential for human health. Therefore, enriching soils in nutrients not only addresses food security and economic issues by increasing crop yields, but it also addresses equally vital nutrient security issues. Agricultural practices that do not restore trace nutrients such as zinc, copper, and manganese to the soils and only seek to grow calorie-rich food crops may provide hunger relief but can exacerbate regional malnutrition problems. Micronutrient malnutrition (particularly deficiencies in iron and zinc) is rampant throughout the developing world and under-resourced communities in developed countries. Soil remineralization with rock dust or agromineral mixtures addresses both food security (hunger relief) and nutrient security (malnutrition) challenges.

Tanzania hosts a vast supply of rock types with excellent nutrient profiles that have been known to improve soil quality since the early 1980s.  The compositions (nutrient profiles) of some promising Tanzanian source materials are shown in the following Table. Note the relatively high levels of key nutrients such as calcium, magnesium, potassium, and phosphorus. These rocks also contain tens to hundreds of parts per million of zinc, nickel, copper, and boron, all of which are essential micronutrients. 

Over the past few decades controlled scientific studies have shown that soil remineralization through the addition of rock powers can reverse soil degradation, enrich beneficial microbial communities and  improve crop yield, nutrient density and plant resistance to pests and disease. Based on the strong scientific underpinning, several commercial brands of rock dust soil remineralizers have been developed and certified for use in several countries.

In most environments, mineral weathering is a slow process, so to speed up the supply of nutrients to soils, the rock materials used for remineralization are ground into a fine powder, which greatly increases their dissolution rates. Mixing rock powders with organic materials such as compost can also accelerate their dissolution as organic acids, and microbes from the organic material catalyze the breakdown of chemical bonds within the minerals. Incorporating rock dust into composts can be particularly effective for soil remineralization because the organic acids and microbes interact with the elements released from the dissolving minerals and convert them into molecular and ionic forms that plant roots can readily absorb. David Paul and EWB-Tanzania’s plan for developing a locally sourced soil remineralizer involves mixing the nutrient-rich volcanic rock dust with organic materials to take advantage of these beneficial effects.  

A Tanzanian Sourced Soil Remineralizer: Rutubisha

The new nature-based, Tanzanian agromineral mixture being developed by David Paul and EWB-Tanzania has been named Rutubisha, which is a Swahili word meaning “to apply nutrients” or “to remineralize.”  The Rutubisha product will include locally sourced alkaline volcanic rocks (including basalt) from the Manyara and Mbeya regions, mica and feldspar from the Morogoro region, and calcite lime from the Tanga region limestones. The general locations of the source materials are shown on the map below.  

All of these rock types and minerals that will go into Rutubisha (basalt, alkaline volcanics, mica, and feldspar) have been well-studied as agricultural amendments in other locations. For example, research in the early 1980s quantified how crushed basalt improved the phytoavailability of calcium, magnesium, and potassium and cation exchange capacity in tropical soils. In more recent studies with Maize and bean plants, basalt was found to increase the availability of phosphorus, potassium, calcium, and magnesium levels by greater than ten times relative to control tests. The basalt led to crop accumulations of macro and micronutrients up to five times higher than plants grown in soils without basalt amendment.  Tanzanian basaltic scoria (a highly porous, pumice-like volcanic rock) was also effective as a slow-release fertilizer and inorganic mulch to retain soil moisture, as shown by the pioneering Tanzania-Canada agrogeology project in the 1980s.  

Other alkaline volcanic rocks common in Tanzania, such as phonolites and nepheline-bearing lithologies, have shown great potential as soil remineralizers that provide a long-term supply of phosphorus, potassium, manganese, zinc, and copper.  In fact, volcanic rocks, in general,  have been shown to be crucial to overcoming the agricultural crisis caused by the disruption of global fertilizer supply caused by war and unrest. Basalts, phonolites, and nepheline-bearing rocks are all common in the volcanic regions of Tanzania. 

Micaceous minerals (e.g., phlogopite) from pegmatites mined in the Uluguru mountains of the Morogoro region are rich sources of potassium, magnesium, calcium, manganese, and zinc. Research in the 1980s and 1990s showed that phlogopite mica was an effective agromineral, increasing rice yields by over 41% compared with other soil additives such as potash (soluble potassium salts). More recent studies have also shown the promise of other types of mica as natural remineralizers.  

As early as 1945, ground potassium feldspar was shown to be an effective fertilizer in forest nurseries. Other studies have shown that hydrothermally altered potassium feldspars are at least as effective as potassium chloride potash. Potassium feldspars from the Uluguru mountain pegmatites will be used in Rutubisha as a slow-release source of potassium.

As mentioned above, the rock powders will also be mixed with local organic materials such as compost manure and biochar (a charcoal-like material made by burning agricultural and forestry wastes). The Rutubisha development will be guided by the wealth of existing scientific literature and practical experience with agromineral soil amendments, such as the pioneering Tanzanian agrogeology study performed by professors Ward Chesworth and  Peter van Straaten of the University of Guelph in Ontario, Canada and professor Johnson-Semoka of the Sokoine Agricultural University of Agriculture in Morogoro Tanzania.

Rutubisha as a Sustainable Solution

As envisioned by David Paul and colleagues at EWB-Tanzania, the practical solution to the problems facing Tanzanian agriculture is to support farmers with locally sourced, nature-based fertilizer (Rutubisha) that remineralizes depleted soils and therefore increase crop yield and nutrient density. Increasing crop production yields and produce quality will allow farmers to sell more of what they grow, improving local economies, and will address nutrient security by increasing the supply of nutritious fruits and vegetables. 

Remineralization also fights climate change, especially in combination with biochar, a carbon storage form that persists for up to two thousand years. Biochar is widely available in Tanzania and can be mixed with local rock powders to provide a long-lasting carbon source in remineralized soils. Rock powders also sequester carbon through soil carbonation reactions. The weathering of mineral powders in the soil converts carbon dioxide into non-gaseous, geologically stable forms of carbon such as bicarbonate ions (HCO₃^–). Carbonate ions are basic molecules that counteract acidity as they are transported through soil solutions into local water bodies and eventually to the oceans, where they counteract seawater acidity. Marine organisms use carbonate ions to form their shells. Both organic and inorganic carbonate mineral precipitates are deposited over time to form limestone, which can keep carbon out of the atmosphere for millions of years. 

The soil remineralization project envisioned by David Paul and EWB-Tanzania will have seven major impacts, all of which are identified as central United Nations Sustainable Development Goals. These are summarized in the following table.

Making Rutubisha A Reality

David Paul has begun laying the groundwork for EWB-Tanzania’s nature-based agromineral development project. As shown on the map above, the regional sources of promising agromineral components have been identified. These sources are located in Mbeya and Manyara regions for alkaline volcanic rocks (such as basalt), the Morogoro region for mica and feldspars, and the Tanga region for calcite from limestone. Organic sources of carbon, nitrogen, and phosphorus, such as compost manure and biochar, will also be locally sourced and combined with the agrominerals as needed. 

A general plan for the project activities has also been sketched out. This is shown schematically in the flow diagram below.   

The mineralogy and chemistry of all agromineral materials will be characterized at the Southern and Eastern African Mineral Centre (SEAMIC) at the African Minerals and Geoscience Center in Dar es Salaam. The chemical compositions will be used to screen out any materials with high levels of toxic metals and will allow Rutubisha team to carefully formulate and customize the nutrient profiles of the agromineral mixtures. The ratios of the different materials will depend on the remineralization/restoration needs of a particular soil. This customization of the Rutubisha mixtures will be guided by agronomists and geoscientists from partner institutions: Sokoine University of Agriculture –Tanzania, Tanzania Agricultural Research Institute, and Remineralize the Earth. 

The locations for the initial Rutubisha processing center and field test plots have also been established (indicated by the red star on the map shown above). Field tests will be used to optimize the agromineral mixtures and to quantify and demonstrate their efficacy on a working farm in the semi-arid, eastern agro-ecological zone. The initial test plots are located near Dakawa Village in the Morogoro region. This spot provides several geographic advantages, such as easy access to the Wami River, close proximity to several smallholder farms, and easy access to a main road for easy transport of materials. After successful trials at this location, Rutubisha mixtures will be tested on working farms from each of Tanzania’s other major agro-ecological zones. 

The Rutubisha agromineral materials may be new to local farmers, but the way they are spread and worked into the soil will be similar to traditional methods used for other amendments such as manure, lime, and organic composts. In fact, the simultaneous application of compost and rock powders will likely be the most efficacious way of incorporating the Rutubisha mixtures into the soil. For example, the application of rock dust mixed with compost to apple orchards in China was found to improve soil nutrient levels (including calcium, magnesium, magnesium, zinc, and boron) and also enhanced the activity of beneficial microbes. The new method of combining rock dust with traditional compost led to a significantly increased apple crop yield and improved vitamin C levels in the fruit.  

So an important principle for implementing the Rutubisha project is to respect traditional agricultural practices. The project seeks to complement and build on the wisdom of Tanzanian farmers who have an innate knowledge of the particularities of their land and local climate dynamics. The goal is to work collaboratively and collectively to discover and implement sustainable and regenerative farming methods that will lift smallholder food growers out of subsistence poverty. 

There is still a lot of work to be done in making David Paul’s vision of a nature-based, low cost and locally available fertilizer a reality. But the work is underway. Given adequate resources, the Rutubisha project could play a key role in revolutionizing Tanzanian agriculture by providing a sustainable, self-sufficient pathway to restored and remineralized soils. With healthy soils, crop yields increase, crop nutrient density improves, and growers can move beyond subsistence farming to start small businesses providing jobs and nutritious food throughout Tanzania.    

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.