Abstract
Tea (Camellia sinensis L.) is the most widely consumed beverage in the world. It is mostly grown in the tropics with a heavy dependence on mineral nitrogen (N) fertilisers to maintain high yields while minimising the areas under cultivation. However, N is often applied in excess of crop requirements, resulting in substantial adverse environmental impacts. We conducted a systematic literature review, synthesising the findings from 48 studies to assess the impacts of excessive N application on soil health, and identify sustainable, alternative forms of N management. High N applications lead to soil acidification, N leaching to surface and groundwater, and the emission of greenhouse gases including nitrous oxide (N2O). We identified a range of alternative N management practices, the use of organic fertilisers, a mixture of organic and inorganic fertilisers, controlled release fertilisers, nitrification inhibitors and soil amendments including biochar. While many practices result in reduced N loading or mitigate some adverse impacts, major trade-offs include lower yields, and in some instances increased N2O emissions. Practices are also frequently trialled in isolation, meaning there may be a missed opportunity from assessing synergistic effects. Moreover, adoption rates of alternatives are low due to a lack of knowledge amongst farmers, and/or financial barriers. The use of site-specific management practices which incorporate local factors (for example climate, tea variety, irrigation requirements, site slope, and fertiliser type) are therefore recommended to improve sustainable N management practices in the long term.
Highlights
Tea is the most widely consumed beverage in the world [1] and is made from the dried new leaves of the Camellia sinensis (L.) plant, an evergreen shrub [2,3]
Additional N can increase yields and the quality of green leaf tea, whereas the quality of black tea is reported to decline at high N applications
Excessive and imprecise use of N fertilisers to increase tea yields has resulted in negative impacts on the environment such as soil acidification and the leaching of N into surface and groundwater, leading to eutrophication
Summary
Tea is the most widely consumed beverage in the world [1] and is made from the dried new leaves of the Camellia sinensis (L.) plant, an evergreen shrub [2,3]. In 2019, the global tea production was approximately 6.49 Mt, with 42% being exported with a value of about 15 billion USD [4,5]. In 2019, the largest tea producers globally were China (2.77 Mt), followed by India (1.39 Mt), Kenya (0.46 Mt), and Sri Lanka (0.30 Mt) [4]. The entire tea sector is projected to reach a retail value of about 73 billion USD by 2024 [7]. In order to maintain high levels of production to meet demand there will be an increase in dependence on high N fertiliser inputs. This is likely to have significant adverse environmental consequences resulting in an urgent need to identify and implement alternative practices
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