EFFECTS OF FERTILIZATION ON TEA

Manure for agricultural purposes and tea fertilization is fundamentally comprised of three main chemical components referred to by the symbols N-P-K. ‘N’ stands for Nitrogen, ‘P’ stands for Phosphorous, and ‘K’ stands for Potassium. In this combination, nitrogen is termed ‘leaf manure,’ in accordance with its efficiency in aiding the growth of large and soft foliage. Phosphorous is accredited with its capacity to reinforce the growth of seeds, flowers and fruits, hence the attribution ‘berry manure.’ Potassium benefits the growth of strong and thick roots, branding it as ‘root manure’.[1]

These three components together form the foundation for the growth of any plant and it is through adjusting their proportions that a farmer can regulate the growth and outcome of his crops. The proportions depend on the requirements for each different plant species, and in the case of tea it is not the fruits of the plant, but rather the leaf of the bush the producer aims to obtain. Therefore, when creating suitable manure for a tea garden, the focus is placed on a high amount of nitrogen with smaller amounts of Phosphorous and Potassium to serve as a support.

Tea fertilization and amino acids

tea fertilization

When the tea bush absorbs nitrogen from the soil as nutrition for its growth, it transforms the substance into amino acids. These amino acids are transported through the stem and twigs to feed the development of new buds and leaves. In the early 20th Century, Japanese scientist Kikunae Ikeda [池田菊苗, 1864-1963] discovered a taste in kelp stock, a seasoning often used in Japanese cuisine, that hadn’t previously been named. This taste was attributed to a chemical component known as glutamate, which in essence is an amino acid similar to the L-theanine amino acid present in most variations of green tea. He attributed the name ‘umami’ to his discovery and made it the fifth addition to the four tastes salty, bitter, sour and sweet that were already recognized. Umami is a savory taste that is not palatable by itself, but makes a wide variety of foods such as tomatoes, mushrooms, seaweed, soy sauce, meat, and Parmesan cheese, taste pleasant. It is said to have a mild but lasting aftertaste which is associated with induced salivation and a sensation of furriness on the tongue, stimulating the throat, the roof and the back of the mouth.[2] A chef once told me that the presence of umami flavor in food could be sensed in the mouth as a light greasiness on the tongue and inner cheeks. This feature is distinguishable indeed since most of the foods that contain umami don’t contain any form of grease or oil otherwise. And it is this sensation of ‘deliciousness’ that Japan’s contemporary green tea consumers value most in their national beverage.

In return, the tea industry places immense focus on delivering a crop that is imbued with umami flavor, and to do so research on the use of manure to increase the amino value in the tealeaf has excelled in recent years. In post-war Japan a monosodium glutamate (MSG) sold under the brand name ajinomoto [味の素] became immensely popular, and was indispensable in most households. MSG is known to contain high amounts of amino acids, and because of dependency on this flavor by the population, a range of biased tea vendors adopted the wrongful practice of adding ajinomoto to their teas merely by means of appealing their product to the masses. Luckily such actions have now become condemned, but the focus on the umami flavor in tea remains strong.

Protection from photosynthesis

In the past the amino value of the tea was regulated through shading practices protecting the leaf from photosynthesis, and by small amounts of organic fertilizer. Today the focus on soil amendment has become the foremost reliance for umami regulation. However, the use of fertilizer cannot be seen in disconnection from shading practices. When high amounts of nitrogen are added to the soil, the resources for the tea bush to generate amino acids increases, leading to a higher than usual amount of amino acids present in the tealeaf. Considering that amino acids are the main source for the creation of catechin through the process of photosynthesis, it is apparent that a higher amount of amino acid in the leaf would simultaneously point to a higher amount of catechin, and thus bitterness, in the final product. When intense tea fertilization is combined with dedicated shading practices, the high amounts of amino acids in the tealeaf can be contained. However in the case of sencha – which now too has become subject to a preference for umami flavor – no shades are used in orthodox farming methods.

In Japan it is common knowledge that mainstream gyokuro must be brewed at a temperature as low as 60 or even 50 degrees. Kabusecha should be brewed at approximately 70 degrees, and sencha should at the most be brewed at a water temperature of 80 degrees Celsius. Brewing these teas at a temperature warmer than indicated could mean that the final brew becomes too bitter to be palatable, and at the right temperature the amino acids that are desirable for a delicious taste are adequately released. These brewing methods originated as a result of contemporary fertilizing practices that artificially induce amino acids in the crops, thereby inevitably also engendering a larger amount of catechin in the end result. Research has pointed out that although catechin doesn’t release from the tealeaf under 80 degrees Celsius, amino acids continue releasing at any given temperature.

Such brewing methods are an indication of the influence of contemporary cultivation practices on the consumption and appreciation of tea. And, to return to our main topic, the reason why a contemporary sencha shouldn’t be brewed at a temperature higher than 80 degrees Celsius is merely because its growth under the open sky has converted most of the amino acids that were added to the bush through tea fertilization, into catechin through photosynthesis. Moreover, since recent years, sencha producers now also have increasingly begun to apply brief periods of shading on sencha bushes to maintain a higher amino value. To conclude, contemporary fertilizing practices depend on the addition of nitrogen to the soil to induce higher amounts of amino acids in the tealeaf. The preference for umami flavor with the consumer has sparked the tea industry to research methods to artificially encourage a higher amino value in the finished product, leading to practices that change the way tea is consumed and appreciated. In addition, this also generates a new problematic I haven’t touched on yet, which is the environmental issue unnatural fertilizing, and consequentially pesticide applications, brings about. I have termed this ‘the vicious circle of contemporary tea farming’. Enhanced flavor through tea fertilization attracts more bugs. Therefore, when one wishes to obtain a tea with an enhanced taste, one must also deal with the increased threat from unwanted visitors, calling on the unfortunate application of agricultural chemicals to repel bugs and prevent disease.

[Case study] An example of how fertilizer is prepared and applied – Azuma

[Case study] The maliciousness of agricultural chemicals – Tokuya


[1] This threefold of components termed by their individual capacity was taken from the terminology in Japanese that is used in common language under manufacturers. Leaf manure is pronounced hagoé [葉肥], berry manure is named migoé [実肥], and root manure, negoé [根肥].

[2] For further reading about the properties and specific traits of the umami flavor, refer to Yamaguchi S (1998). “Basic properties of umami and its effects on food flavor“. Food Reviews International. 14 (2&3): 139–176.

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