Facts about Sustainable Potassium Management

Sustainable Potassium Management

Potassium is the second most abundant nutrient after nitrogen, but despite this abundance, potassium is not always available in a form that can be used by plants. Globally around a fifth of all agricultural soils face severe potassium deficiency. There is a growing recognition of the importance of potassium and a need to increase our knowledge of its biogeochemical cycle

What is sustainable potassium management and why do we need it?

Potassium (K) is the third of the indispensable macronutrients required for all life, alongside nitrogen (N) and phosphorus (P).
Insufficient potassium in the soil is a threat to global food production and to achieving Sustainable Development Goal 1: Zero hunger.
Sustainable potassium management requires further information on potassium and its potential effects to the environment due to overuse or inaccessibility.

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What is potassium?

Potassium is a soft alkali metal, that is unstable on its own and reacts easily with air and water, that tends to occur combined with oxygen or different minerals.
There is no gaseous form of potassium
Potassium can be found in many different types of rock in small concentrations.
Hundreds of millions of years ago under hot, dry climatic conditions, deposits were formed from saltwater lagoons. These deposits form the larger, more commercially viable potassium deposits that are the target of potassium mining today and primarily for agricultural fertilizer.

Where can potassium be found?

Historically potassium was extracted from wood ash, which was then crystallized in pots to extract the potassium, hence the name ‘potash’. Today potash is also used to describe mined potassium salts, which are mostly mined as potassium chloride (KCl).
The current extractable global reserves of mineral potassium occur in a handful of countries, predominantly in the northern hemisphere with around half of these reserves found in Canada alone. The reserves of potassium that can be mined for producing potassium-based fertilizers are believed to be sufficient to meet the projected demand for centuries.
It is estimated that in 2025, 69 million tonnes of potassium will be produced, which is over 50% more than the expected demand by 2025.
Despite there being adequate reserves, the fact that these are in only a few geographic locations presents logistical and cost challenges in getting this resource to where it is needed, resulting in inequity in its access and availability.
Useful quantities of potassium also occur in some ocean algae, like kelp. Kelp can yield between 3 and 10% available potassium which can be processed and used as a liquid fertilizer.
There can often be quite a lot of potassium in soils, but only a small proportion of this is available to plants. The availability and uptake of potassium is affected by soil moisture, oxygen levels and soil temperature.
Since potassium is soluble it does not remain for long in the soil and is easily leached out.
The characteristics of this nutrient are important to understand in fertilizer application to ensure it is applied at the right time and at the right dose, to avoid unnecessary economic costs to the farmer.

What do we use potassium for?

In 2021, 45 million tonnes of potassium was used globally. Around 95% of this was used for agricultural fertilizers, which represents a US$15 billion industry and equates to around 20-25% of total fertilizer consumption.
The potassium can be formulated to create a combined Nitrogen, Phosphorus and Potassium (NPK) fertilizer, or as a separate potassium-specific fertilizer, such as potassium chloride.
Like other nutrients (i.e., nitrogen and phosphorus) potassium is an important limiting factor for plant growth and deficiency can threaten food security.
Potassium is required in large amounts for growing crops. Plants with enough potassium cope better with adverse conditions such as drought, frost damage, insect and disease attacks.
The global demand for potassium was increasing at 2.4% per annum between 2015 and 2020 to meet the growing need for food production and biofuels.
Potassium has other uses, including serving as an additive in animal feed, food additives, in the beer brewing process, water softeners, de-icing solutions, glass and textile manufacture, pharmaceuticals and explosives.
Historically saltpeter (KNO₃) was used in gunpowder.

What is the issue?

The environmental impacts of using potassium fertilizers on soils, water and air are not well understood, but we do know that potassium can be lost to the environment through erosion, leaching, burning and harvesting of crops.
Unlike phosphorus and nitrogen, no specific environmental concerns have been identified from losses of excess potassium, although overfertilizing could result in unnecessary costs for the farmer.
Mining potassium can generate millions of tonnes of refuse, which includes sodium chloride salts that can leach and contaminate soils and fresh water, impacting biodiversity. It also results in the emission of methane, carbon dioxide, and nitrous oxides, which are all potent greenhouse gases.
Globally around one-fifth of agricultural soils face severe potassium deficiency. Potassium deficiency can be caused by not fertilizing at the recommended application rates and can threaten food security.
In the case of the Mediterranean Basin a negative potassium balance is caused by the need to increase food production with increasingly arid conditions and declining potassium. In such cases, potassium fertilizer is the limiting factor for food production.
Inequity of access is the main cause of under-fertilization. This can be due to highly volatile prices, geopolitics, the lack of local sources and the high cost of imports and transportation, particularly affecting farmers in developing countries.
Lack of access to potassium fertilizer means that despite 25% of available potential croplands being on the African continent, the African share of global potassium fertilizer consumption is only 1.7%.
The impact of climate change on the potassium cycle is so far not known, but understanding the implications on potassium availability and plant uptake could be particularly important to meeting food production needs, particularly in arid and semi-arid regions given projected increases in extreme weather conditions.

What are the solutions for sustainable potassium management?

There is a growing recognition of the importance of potassium and a need to increase our knowledge of this biogeochemical cycle. Four types of actions could help take pre-emptive steps towards sustainable potassium management:

Reduce dependence on mineral potassium fertilizers
•    Promote the use of organic fertilizers.
•    Transition to small-scale closed-cycle agricultural production, where fertilizer nutrients are produced from farm wastes using manure, crop residue and compost. For example at harvest rice straw contains around 15 kg of potassium per tonne and wheat straw around 10 kg of potassium per tonne.
•    Use soil testing to better understand and improve soil health.
•    Increase targeted use where there are potassium deficiencies and use the 4 Rs of nutrient management – the right source, right rate, right time and right place.
•    Changes in consumer behaviour – such as choosing a more plant-based diet and reducing food waste can help to reduce how much fertilizer is needed in the first place.

Promote principles of circularity
• Potassium is not widely recovered and recycled. Circular thinking could increase efficiency in how potassium is used and recycled. Policies that support circular principles would be a priority.
• Whilst there are rather low quantities of potassium in wastewater fractions, there are a few existing examples of nutrient recovery technologies that produce potassium outputs:
o Recovering potassium chloride from fly ash produced from municipal waste
o A nitrogen-potassium fertilizer solution produced from liquid manure and water treatment effluent that can be used for hydroponics.

Invest in identifying new sources of potash
• Expand conventional sources of mined potassium, including searching for potash deposits in the global south to increase accessibility.
• Explore low-grade but indigenous potassium bearing minerals as locally accessible alternatives to high-cost imported potassium fertilizers.

Other potential solutions
• Increase the availability of potassium that is already in the soil by using microorganisms to activate it so it can be used by plants

20%

Globally

1/5

One fifth of all agricultural soils face severe potassium deficiency

Related Sustainable Development Goals

Did you know?

If oceans were a country, they would be the seventh largest economy in the world.

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