Every year Kenya’s 680,000 tea farmers sacrifice some of their October tea bonus pay to buy chemical fertilisers, they are decimating their soils to the point that their yields have halved. To reverse this damage and double their output, farmers only need to start adding manure to their soils.
The country’s tea farmers produce less than two kilograms of leaves for every tea bush according to the Kenya Tea Development Authority. This translated to a production of 2,030 kilograms per hectare in 2018 which is less than half what mature tea plants should give. A key driver to this low production is the extreme acidity of tea soils in Kenya which have been recorded to have a pH as low as 3.09 brought on by repeated nitrogen fertiliser application. In experiments done in China, tea soils that started as highly acidic because they were only fed on chemical fertilisers but were switched to both organic and chemical fertilisers saw their yield increase from 2,630–3,145 kilograms per hectare to 4,928-5782 kg/ha over five years as their soils became less acidic.
After the announcement of the tea bonus, the other big ticket item on the calendar of Kenya’s tea farmers is the price and the date tea fertiliser will be issued. This is because tea trees are heavy feeders as they are harvested on an almost daily basis and need to be pruned every October/November.
The Tea Research Foundation of Kenya recommends farmers apply 300–600Kg of primarily nitrogen fertiliser per year for a hectare of mature tea, however, farmers will often apply much more than this in the hopes that this will bump up their yields. This is especially the case now that the prices of KTDA-distributed fertilisers are capped at Sh2,500 for a 50 kg bag.
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While nitrogen fertilisers give farmers a short-term bump in their yield, with every application they also make the soil more acidic and less fertile. In Timbilil Tea Estate in Kericho, tea given 240 kg/ha of nitrogen fertiliser between 1985 and 2017 saw its soil organic matter content fall and after 32 years, the amount of tea produced did not increase even after the amount of fertiliser it was fed on went up. This shows that only giving tea chemical fertilisers eventually does more harm than good.
This is not only a problem for Kenya farmers, but one affecting the world’s tea farmers. Due to years of nitrogen fertiliser application, farmers with tea bushes that are 40 years have seen their harvest fall consistently in the past two decades. This is a wake-up call for KTDA’s 680,000 small-scale farmers who the company’s Manager for Sustainability and Certifications Kanja Thuku admits are growing tea bushes that are older than 50 years.
While tea is known to thrive in acidic soils, the crop produces the best in soils that have a pH range of 5.13-5.33 soil pH. Once the soil’s acidity falls below a pH of 4.5, its growth is diminished as it produces fewer new roots. The lack of a well-developed root system then contributed to a reduction in the amount of food the plant took in and how well it was used which eventually decreased the yield and the quality of tea produced.
Applying sheep, goat manure, or a mixture of cow manure and rape cake by digging it 50 centimeters deep around the roots of tea trees brought the roots back to life, improved their absorption of nutrients, and in turn improved the yield and quality of tea trees.
Five tons of this well-decomposed manure or compost is added to a hectare just before the rains to help the manure sink into the soil. In mature tea bushes, one or two manure applications should be done every year when the tea is still being plucked and fed the most.
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The manure should be spread around the base of each tea tree a few centimeters away from the stem to prevent rot.
120-150 kilograms of NPKS 25:5:5:5 or NPK 20:10:10 fertiliser is also added for every hectare per year.