Special K: potassium production
Oliver Heidrich, Brett Cherry, Natalia Yakovleva, David Manning and Alistair Ford look at how the Global South could adopt more local potassium production, rather than relying on the northern hemisphere.
Fertilisers are routinely added to soil to enhance plant growth and increase crop yields. They include three main macronutrients: nitrogen (N), phosphorus (P) and potassium (K). If any of these macronutrients were to become unavailable or inaccessible to agriculture, a global food crisis of unprecedented scale would likely ensue.
Potassium is integral to plant growth and animal health, but it is a non-renewable resource. Unlike nitrogen and phosphorus, whose supply and recycling details are well-documented, little is known about the potassium supply and consumption cycle. Although potash, the raw material used to produce potassium fertilisers, is abundant, it is located in the northern hemisphere, meaning its availability in the tropics involves a high transport cost.
By 2050, global demand for grain is expected to have increased by 60%, while global cropland area will have increased by only 10%. Estimates show that crop production needs to increase by 25%-70% above current levels to meet 2050 demand, but emissions and nutrient losses must drop dramatically in order to restore and maintain ecosystem functions. Can countries work together to close yield gaps in the Global North and South in order to feed humanity by 2050, when the global population is expected to exceed 9bn?
If agriculture and soils in the southern hemisphere are to reach the outputs required to feed their populations, local alternative potassium supplies need to be developed. At present, potassium fertilisers in the form of potash are derived from soluble salts mined in the upper parts of the northern hemisphere. From there, they follow a one-way stream from production to agriculture to human food consumption to waste disposal. No effective method for potassium recovery or recycling exists, although crop residues do provide one input (see Figure 1). Most of this vital mineral is mined in just a handful of countries – Canada has 53% of world potash reserves; Canada, Russia, Belarus and Germany combined have 92%. From these places, potash is shipped around the world to fertilise crops.
Agricultural mineral resources in the soil are depleting faster than our ability to put them back into the land. On a global scale, the problem is complex. Soils in tropical countries are highly weathered and tend to have a low nutrient content. Rapidly growing populations in Africa have limited or no access to the fertiliser needed to replenish their soils, while in South America, Brazil is one of the top food exporters in the world and one of the largest fertiliser consumers. China is the largest consumer and importer of potash from the Global North, which covers 70% of its demand. The south of China is generally short of potassium, resulting in annual potash imports of about 6m tonnes. If agriculture is to support a growing global population, local alternatives may be worth considering.
To date, there has been no rigorous agronomic research or survey of the potassium status in Africa’s tropical soils. Potassium deficiency has affected maize, rice, cassava, fruits and vegetables. This is a problem not only for Africa, but also for countries that depend on its food exports – including the UK. Food consumers in the UK rely on foreign sources of food, crop and animal feed, and this dependence could increase in the future.
In 2016, just over half of the UK’s food supply originated outside the country, including 30% from the EU, 5% from Africa and 4% from South America. After Brexit, if the UK’s food imports originate less from the EU and more from countries in the Global South, the gaps between nutrient outputs and fertiliser inputs could widen (Figure 2).
The UK is effectively mining nutrients from soils in the world’s poorest countries, which have no local fertiliser production. This makes food supplies even more vulnerable – especially when factoring in ongoing pressures such as climate change, which pose a significant risk to global food security. There are, however, opportunities for countries with no local fertiliser production to establish it, especially where there are known deposits that could be mined.
In many low and middle-income countries, minimal fertiliser is used for growing crops. Zambia uses the most fertiliser in sub-Saharan Africa, for example, at 46.2kg per hectare. This figure pales in comparison to the amount used in EU countries – 160.1kg per hectare. Latin America and the Caribbean use 127.9kg per hectare, and North America uses 126.6 kg per hectare. Countries with low fertiliser production should not necessarily be raising their fertiliser input to the same level as those with high inputs, because overuse is undesirable for increasing yields over the long term. To sustain the global food supply, fertiliser inputs will need to increase, but potassium inputs may need to double to compensate for what is removed by crops. In addition, intensification of agricultural lands is likely to be required in order to feed the rapidly growing populations in the developing world.
What can be done about this global challenge? Local potassium fertiliser production in the Global South is urgently needed to enable agricultural systems in developing countries to feed local populations. National governments need to support geological exploration of potassium-bearing minerals such as potassium feldspar in Malawi, Ethiopia and Eritrea. It’s clear that the problem of potassium deficiency and other mineral resources for agriculture are not merely
a global trade concern, and that much work remains to be done.
Geologists, agronomists and soil scientists must drive forward scientific initiatives to identify new potassium-bearing minerals and explore conventional mineral-based fertilisers in developing countries. Agronomic knowledge also needs to increase to allow us to understand the potassium status of soils, especially in Africa. This approach has been pioneered in Brazil, where the use of novel locally derived ‘remineralisers’ is federally regulated.
In addition, new markets need to be developed for alternative potassium fertilisers – a process that requires scientists, policymakers and economists to work together. The UK and EU countries stand to benefit from working with the Global South to secure food supplies both locally and globally. They can do this by discovering and investing in innovations such as mineral recycling, alternative mineral resources and alternative farming practices that improve soil quality and maximise yields.
Scientific and policy leadership from the UK could help the developing world reach targets for the UN Sustainable Development Goals, to make potassium consumption and production responsible and sustainable. We must understand the impact that local consumption has on the global market – not just for potassium, but also for the other minerals and nutrients needed to maintain a healthy diet.
The authors are members of and contributors to the Global Challenges Academy at Newcastle University.
Seeking alternative sources
Producing fertilisers for agriculture can be an energy-intensive chemical process, especially for nitrogen and phosphorus. With lower energy costs, mined potash is used to produce potassium chloride, the main fertiliser product used to increase crop yields. Animal feed also requires potassium fertilisers. Between 1964 and 1997, animal protein consumption more than doubled in developing countries, from 10kg/year to 25kg/year; it is expected to reach 36.7kg in 2030, which is still low compared to the 79kg of meat the average person in the UK consumes each year. Local alternative mineral sources that are slow-releasing and cheaper than traditional ones would make global food production more secure.
Alternative sources of potassium include polyhalite, nepheline, potassium feldspar and verdete. Through cooperation between governments and industry, these could be used to produce crop fertilisers. Potassium feldspar and nepheline exist in several African countries, including Malawi, and the former has been investigated as an alternative source of potassium for developing countries – it is locally produced and obtained through green chemistry processing. In Brazil, silicates are an alternative source of potassium for crop production, as is carbon sequestration.
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