African farmers return rapidly declining soil potassium with ancient ash-in-pot technology

Farmers are turning to an ancient technology to return potassium to their soil on evidence that they are losing 10 per cent of the mineral which is vital to plant growth after each harvest.

Potassium being used up far quicker than it can be returned to the soil presents Africa’s agriculture with a disaster in waiting according to soil science expert David Manning. Potassium is the K in NPK fertiliser with the rest being Nitrogen and Phosphorus– the three main fertilisers used in farming. “All of the potash used in making potassium in the fertiliser that lands in Africa is mined outside of the continent. Most African countries cannot get enough potash let alone afford it to blend in potassium fertiliser. This, in turn, means most farmers cannot afford the price of buying potassium fertiliser,” he explained. According to the Newcastle University professor, the world potash production would have to more than double to match its current demand.

Potassium is used by crops to make their food, reduce water loss, strengthen plant cell walls reducing how often they are infected with diseases. It is loved by all crops but especially by potassium-hungry crops like tomatoes, carrots, and potatoes. Researchers have shown that fungi, bacteria, insects, and mites are reduced by 67.3 per cent through proper application of Potassium. It also improves the quality of crops by increasing the size, weight, color, and taste of fruits, grains, and vegetables, and promotes uniform ripening and longer shelf life of produce. It also encourages root development and helps plants withstand stresses like drought.

The potash used in fertiliser is mined from natural salt that was in seas that evaporated millions of years ago. 78 per cent of the world’s potash is gotten from Canada, Belarus, Russia, and China. It is taken off the ground as pink or red rocks and made into white, pink, or red potassium fertiliser. 

According to data gathering site Statista, Potassium is the third most used fertiliser in Kenya.  Farmers used an estimated 42,700 tonnes of the fertiliser in 2019. This still remains low as studies have found that Kenyan farmers apply just 3.62 kg/ha of potassium which is well below the recommended 20-100 kg/ha which gives the most grain yield.

Farmers can however add to the amount of potassium in their farms by making their own potash from locally sourced material.

Potassium had been produced by farmers as early as the 1700s by burning trees, mostly hardwood and broad-leaved trees, and wood left after clearing forests then dissolving the ash left behind in large pots of water, hence the name, “pot-ash”. This was fed back to the soil to make it healthier. It was also used to make food sweeteners and animal feed supplements or further refined to make soap and used as part of the manufacturing of soil fertiliser and glass. Potash production helped many of the early settlers in North America have a good that they could sell for much-needed cash or credit which helped them clear wooded forests and plant crops.

Wood ash is the world’s best-known source of homemade potassium fertiliser. This is especially the case for hardwood trees such as Grevillea, Eucalyptus, and Oaks contain four to 10 per cent potassium/ potash as well as calcium and magnesium which are also important for crops. By comparison, NPK fertiliser contains 20 per cent potassium.

Softwoods can be used but have less potassium. Ash from treated wood, coloured paper, or painted wood should not be used as it contains harmful chemicals.

Wood potash can be added at a rate of about half a kilogram to one kilogram for every 100 square feet or the size of a small bedroom once every season. 

If you cannot get your hands on wood ash, banana peels are the second-best source of potassium as they contain 42 per potassium oxide after they are dried.

Banana peel potassium is first made by drying the banana peels by laying them in the sun until they are crisp. This makes it easier to burn them as they will produce less smoke. The dried banana peels are then burnt to ash. This ash is not only rich in potassium but also phosphorus and calcium.

This ash can be sprinkled directly around the soil of plants or applied as a liquid by mixing one to two tablespoons of ash in 3.8 liters of water. This needs to be well stirred to make a potassium-rich liquid fertiliser.

Other rich sources of potassium are compost which contains banana peels, chicken manure which may contain up to 1.7 per cent potassium, and seaweed also contains two to three per cent potassium. Stinging nettle tea fertiliser has an NPK ratio of N2:P0:K5 while comfrey leaves which are chopped up with grass and placed as a five-centimetre layer of mulch on the soil provide 0.20 per cent potassium. Every kilogram of molasses also contains 60 grams of potassium.

There is conflicting research on whether natural sources of potassium make the soil too alkaline. To avoid this use homemade potassium fertilisers only according to the recommended doses and preferably after testing your soil’s pH to determine its alkalinity.