From Tea to Sea: Forests, Nutrient Dynamics and Tea Farming

From Tea to Sea: Forests, Nutrient Dynamics and Tea Farming
Written by Jimmy Burridge

Featured image: Chagusaba tea farming at the Kaneroku Matsumoto Tea Garden where grass surrounding the tea fields are cut, dried and laid between plants to fertilize the field and prevent weeds. Photo shows a freshly planted tea field of koshun cultivar plants.

Water vapor rises and floats to the mountains. Rain falls on the mountain, trickles into the soil, emerges at a spring and eventually flows into the sea. Our agricultural practices affect the soil, the water and even how water moves. Both the tea in the mountains and the fish in the sea call us to work with them in a good way. Excellent tea and healthy ecosystems will be the result.


The relationship among humans, forest and water is one of the most ancient, long lasting and fundamental ways in which we impact the world. In this article we survey how people, and their agricultural needs, have interacted with land and waterways, all the way from mountains down to the sea, with a particular focus on tea. We will touch on nutrient dynamics of tea farms and explain how tea production can impact downstream environments. An example illustrates how collaboration between upland and downstream groups of people ensures the proper functioning of the ecosystems upon which they both depend.

Historic forest management 

The history of agriculture in Japan is defined by geology, topography and the dictates of rulers and population centers. Most visibly, successive waves of tree cutting were driven by monument building, city construction, charcoal making and also by peasant needs for their own fuel, building material, green material used for fertilizer and of course for food production. The scholar Conrad Totman has done some excellent research on the forest use and management history in Japan, here is a link to a short article. Most of the material for the section on forest history comes from his work, see references.

The most famous, and perhaps extensive, use of Japan’s most ancient and grand trees were to build the numerous temples, shrines, castles and houses of daimyos and emperors. As empires grew, so did cities, constructed almost exclusively of wood. Since fire, due to escaped domestic cooking fires or warfare, frequently destroyed buildings and sometimes huge sections of cities, more wood would be cut to rebuild.

Large old tree in Otakasan, Toyko PrefectureLarge old tree in Mount Otake, Toyko Prefecture. Photo courtesy of Moé Kishida.


Forest management, arguably the forerunner of modern nutrient management, was undertaken primarily for two reasons; to ensure stable availability of forest products and to prevent negative downstream effects, such as flooding and drought caused by erosion, silting and uneven water supply from the forest. Silting, which occurs when water carries sediment, has the negative effect of immediately lowering water quality for fish and aquatic life and subsequent negative effect on water flow and stream health when this sediment is deposited downstream. This deposition causes the river to become more shallow, and hence wider, slowing the flow and leading to further sediment deposition, a type of feedback cycle. Sedimentation makes low lying fields, such as rice paddies, much more susceptible to flooding. Rulers thus sought to prevent damage to these productive fields by reducing upstream sediment runoff. This, along with the desire to continue to harvest trees for construction, coal and the myriad of other uses pushed forest management in Japan through experiments with conservation, managed cutting, allowance for regrowth, replanting and then plantation forestry.


trees - Moé KishidaTwo images of young, reforested woodland area with primarily one tree species. Left photo in Aichi Prefecture, right photo in Ome, Tokyo Prefecture. Photo courtesy of Moé Kishida.


A more intensive yet dispersed use of forest resources is attributable to farmers, who were of course the majority of the population for most of history. Rural people would gather not just cooking and heating fuel, but also collect wood to make charcoal to sell to urban dwellers. Furthermore, the traditional Japanese farming systems relies on the collection of brush, grass, moss, fallen leaves, basically any compostable organic material, for incorporation into farmland soil. This organic material would decompose and nutrients would slowly become available to the crop plants. For the sake of not romanticizing traditional farmer practices, it must also be mentioned that many farmers would burn the organic material and incorporate the ash, which made the nutrients available much more quickly but obviously resulted in the loss of almost all the carbon thereby contributing to increased atmospheric carbon dioxide levels.

Extensive and intensive tree cutting for fuel and building purposes, notable for cities, temples and houses of the nobility, as well as farmers gathering brush, moss and forest debris, defined and transformed the forest structure, composition and ecology of Japan. One of the interesting examples of the effects of this change in forest structure is how the hiratake (oyster) mushroom, which prefers diverse, mature, fully shaded forests, was replaced around the 13th century by the matsutake mushroom. The matsutake thrives in disturbed landscapes and can grow well in pine dominated forest plantations, which were replaced unplanted diverse forests (Totman, 2000). This link between agricultural expansion, rapid growth of the nobility and the proliferation of matsutake may help explain why matsutake came to be a component of Japanese culture (check out the book “Matsutake, the mushroom at the end of the world” by Anne Tsing, if the relationships between people and mushrooms sounds interesting!). 


Delicate and ephemeral Katakuri- Moé KishidaDelicate and ephemeral Katakuri (Erythronium japonicum, a type of trout lily) flowering in a mixed forest. Photo courtesy of Moé Kishida.


Tea is often grown on the slopes of mountains for the interest of taking advantage of environmental factors often associated with terroir such as temperature swings, morning mist but also due to the practical fact that other crops, such as rice, soybean, buckwheat, fruits etc. are grown on the flat lowlands where their care is much easier. Tea simply lends itself to be cultivated on steeper slopes since each individual row can occupy a separate small terrace. Furthermore, since tea is a perennial crop that does not require tillage and maintains soil cover year-round, it doesn’t contribute to as much erosion as would an annual crop requiring tillage and not covering the soil for part of the year. 


Steep tea field Wazuka, Kyoto prefectureA steeply sloped tea field and monoculture forest in Wazuka, Kyoto Prefecture. Photo by Jimmy Burridge.


Tea production and fertilization

Before the modern era made available synthetic nitrogen fertilizer, tea cultivators relied, like almost all other farmers in Japan, on the aforementioned gathering of organic materials from surrounding areas, including forests, to apply to their fields. In the case of tea, this is termed the chagusaba method, mentioned in this interview. Chagusaba, as well as the more contemporary use of processed bat guano or fish meal as fertilizer, provides a relatively slow release of nutrients that naturally occurring soil microbes also use. However, particularly since the introduction of synthetic nitrogen fertilizer, tea has often been heavily fertilized. Fertilization can promote lush spring grown and can enable multiple harvests. It can also help produce nitrogen rich leaves with plenty of umami flavor. 

As discussed in a previous posts, the umami of high-quality tea is associated with a greater amount of nitrogen rich amino acids. Shading is the classic way to encourage the plant to produce more chlorophyll, the unique molecule that uses sunlight to transform carbon dioxide into sugars, and subsequently into the nitrogen rich compounds that provide the umami flavor. 

Synthetic nitrogen fertilizer comes from splitting atmospheric nitrogen (two nitrogen atoms triple bonded to each other) and then binding the nitrogen to hydrogen to make ammonia, and subsequently other forms of plant available nitrogen. This process requires a large amount of fossil fuel derived energy to create the high pressure and high temperature environment needed for the reactions. While the process was first developed during World War I, it was only used to produce fertilizer at a large-scale after World War II. In Japan, as in many places, this new source of nitrogen fertilizer came at a time of rapid population growth, yet severely depleted forests and traditional sources of nutrients. For that reason, many thought traditional methods could not support the agricultural demands of rapidly growing population, and indeed, at a global scale the spread of synthetic fertilizer enabled millions of people to be fed. In Japan, the use of synthetic fertilizer was encouraged and widely used through the post war years and into the 1990’s.

Tradeoffs of synthetic fertilization

However, this fertilization impacts nutrient dynamics, soil health, ecosystem functioning and even human health in ways that are sometimes negative. The principal ways that fertilization can impact the environment is through runoff, leaching and volatilization. Fertilizer runoff and groundwater contamination via leaching occur when fertilizer is applied to the soil but not absorbed by the plant or bound to the soil before being transported by water out of the root zone. Studies have shown that most of the fertilizer applied to a field, in a high fertilization scenario, is not taken up by the plants and a significant portion is lost to the environment the first year (Chen and Lin, 2016). Runoff of nutrients, primarily phosphorus and the nitrate form of nitrogen (N), from farmland contributes to algal blooms and then eutrophication, which reduces water oxygen levels to the point that fish and other aquatic species actually die. Leaching of nutrients through the soil and into groundwater can similarly lead to elevated levels of nutrients in streams and springs where it can negatively impact riparian ecosystems (Nagumo et al., 2012). 

As readers in the US may be aware, the Chesapeake Bay watershed is subject to intensive fertilizer management, in order to protect the health of the bay. In the past, unintended fertilizer runoff into the bay caused large algal blooms, leading to eutrophication, that in turn harm plant and animal life, including the all-important fishing industry. Several bodies of water in Europe, such as the Baltic Sea, the North-East Atlantic and the Black Sea also have experienced severe eutrophication problems due to excessive nutrients entering from agricultural areas (European Environmental Agency report summary). China also has major problems with excess nutrients harming water quality and ecosystem function.

Volatilization of fertilizer is the process by which a solid fertilizer is transformed to a gaseous form, usually in conjunction with soil microbes and in interaction with soil temperature, moisture, pH etc. Volatilization of nitrogen containing fertilizer can occur in the form of ammonia (NH3) or nitrous oxide (N20). Ammonia emission is a problem firstly to the farmer because the expensive nitrogen that was applied to the soil is literally floating away, and secondly, because when it returns to the soil it can contribute to soil acidification and eutrophication problems. Agriculture, in specific the use of nitrogen fertilizer, is a significant source of nitrous oxide emission, a potent greenhouse gas (Tian et al., 2020). While tea is only about 1% of total farmland in Japan, tea farming is responsible for more than 10% of N2O farmland emissions, meaning addressing N20 emission in tea is very important (Hirono et al., 2021). Research in Japan has studied nitrous oxide emissions from tea fields and offers tools to help understand and eventually reduce N20 production (Hirono and Nonaka, 2012; Zou et al., 2014). 

Soil can also become more acidic due to fertilizing and farming tea (Yan et al., 2018). Acidic soil impacts the soil microbial community as well as root and plant growth. Studies have quantified how water leaching from acidified agricultural land enters groundwater and emerges in springs and streams to eventually impact fish and amphibians (Hirono et al., 2009; Yan et al., 2018). Recent research has broadened the scope of the effects of N fertilization to the soil microbial community and found that N fertilization, possibly in part via acidification, has decreased microbial diversity, weakened microbial community diversity and lowered soil microbial community stability (Ma et al., 2021).

Better management, application methods and products reduce tradeoffs 

Nitrogen application rates increased from the 1960’s through the 1990’s when focus shifted to reducing N application rates and improving nitrogen use efficiency (Hirono et al., 2021). Extensive and long-term environmental surveys of water quality in streams, springs and groundwater in an intensive tea growing region in Shizuoka show a downward trend of nitrate nitrogen in water systems surrounding tea fields since the 1990’s (Hirono et al., 2009). Much work by researchers, agronomists and farmers has been devoted to improve N uptake and utilization efficiency by using new techniques, technologies or simply adjusting the rate, timing and application method (Watanabe, 1995; Wang et al., 2020). Fertilizer management strategies, including limiting runoff from sloped field have been developed (Wang et al., 2018, 2020). Further developments of fertilizer recommendation strategy involve better characterization of the temporal dynamics of nutrient uptake by tea in order to match application with uptake (Tang et al., 2020). Other work has compared identical applications of synthetic fertilizer to a rapeseed (a plant in the brassica family) derived fertilizer and shown the rapeseed derived fertilizer reduces risk of soil acidification and water eutrophication (Xie et al., 2021). Nevertheless, total fertilizer (N and P) applications to tea plantations remains high and risks to surface, groundwater and eventually bays and lagoons and even the sea itself remain (Nagumo et al., 2012).  


Steep tea field, Kiroku tea gardenPrecise and responsible management of steep tea fields at the Kiroku tea garden in Wazuka, Kyoto Prefecture. Photo courtesy of Kiroku Tea Garden.


Linking tea, soil, waterways and the sea

Fishers in Japan have known of the links between the health of the fisheries and the health of agricultural and forest land for decades, and arguably for centuries. Certain coastal  forest are even named ‘Uotsuki-rin’ – ‘fish breeding forests’ (Iwasaki, 2021). Seasonal ceremonies are still practiced that link forest and sea by bringing sea water to a forest shrine (Iwasaki, 2021). In another case, spring snowmelt causes a particular spring at the Nigatsu-dō temple in Nara to overflow and begin its descent to the sea, indicating the beginning of spring (Bedini, 1994). In spite of indicators that people historically knew about the connections between mountains and sea, it took some time to connect the dramatic changes in nutrient dynamics and ecosystem functioning to the introduction of chemical fertilizers.

The Ariake Sea in Kyushu prefecture is a salt water bay receiving fresh water from seven main rivers. It has the largest collection of tidal flats in Japan and demonstrates the challenge of managing nutrients and the interests of different actors. Ariake Bay provides nursery habitat for wild fish, as well as substantial aquaculture activities including seaweed and shellfish (Yagi et al., 2011).  However, its drainage basin has also historically been intensively farmed, and into the present day, much tea is cultivated in the upland regions with vegetables and rice in lowland areas (Shiratani et al., 2005).  As such, nutrient runoff and eroded soil entering the bay has been a challenge that affects fish, shellfish and seaweed cultivation. While innovative water recycling systems, improved upland and lowland farm management and other measures have improved conditions, government agencies, farmers and researchers continue to try to understand and resolve the challenges. 


Two perspectives of a small waterway running through a semi-managed forest in Ome, Tokyo Prefecture. Photos courtesy of Moé Kishida.


As noted above, reduced application rates to tea fields has improved water quality in the Shizuoka region (Hirono et al., 2009), a trend that is likely to be consistent in other tea growing regions of Japan. There is a general movement towards more precise, appropriate and well-timed fertilizer use. A resurgent interest in reconnecting to traditional practices offers further promise to help regenerate healthy ecosystems, as the satoyama movement shows. Satoyama is a traditional agrarian landscape, one in which farmers and foresters modify the landscape and produce a type of mosaic of ecologic systems consistent with the previous couple millennia (Ito and Sugiura, 2021). Some satoyama groups focus on creating the complex human managed landscapes that produce the famous matsutake mushroom (Satsuka, 2014). That groups of young and old people, urban and rural come together to help revitalize traditional practices is an encouraging example of how people and environments can re-learn to live well together. 

An inspiring recent article identified 3784 cases of forest and fishery initiatives supporting better water quality and fish habitats (Iwasaki, 2021). The author outlines several examples, including a reforestation project known as ‘The sea is longing for the forest’ in Miyagi / Iwate, which was initiated by an oyster famer concerned about watershed level ecosystem health. Another example in Kumamoto involves clam farmers, this time in Ariake Bay. The farmers there noticed the negative impacts of upstream soil erosion on their clams and started working with upland communities to reforest sensitive land and reduce erosion. Other projects addressed issues related to seaweed and sea urchin production. Japan is one of the few countries that has these sorts of farmer led initiatives that address watershed health by linking forest and sea. The type of agency and collaboration these collaborative projects demonstrate is very heartening. 


cute forest spirits WazukaPeople making space for cute forest spirits and good luck in Wazuka, Kyoto Prefecture! Photo by Jimmy Burridge.



Now we understand more about how changes in forest species composition, forest age structure and the soil itself effect water retention ability as well as the health and reproductive success of fish and amphibians. Migratory fish that travel upstream to lay eggs can play an important role in bringing nutrients from the sea or downstream lakes, but their migration and reproduction are sensitive to waterway health.

Modern tea production requires nitrogen inputs, even if from organic sources such as locally sourced green manure, spent soybean from soy sauce or miso production, fish meal or bat guano. This can be expensive and synthetic forms in particular, may runoff or leach into groundwater. Good management, which includes proper selection of product, as well as timing and rate of application are important. Many ecologically responsible tea farmers have both reduced fertiliser inputs and improved management. Tea farmers are recognizing the connectivity between tea farming and downstream partners and doing their part to support healthy waterways, which has positive effects on everyone downstream, even fish and fishermen.


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