Friday, 20 November 2009

Effect of global warming on tea production in Sri Lanka

20th November 2009,

By Dr M T Ziyad Mohamed, BSc (SL) Ph D (Sheffield UK), Director, CIC Tea Advisory Services (Pvt) Ltd.,

Tea produced in Sri Lanka commonly known as "Ceylon tea" throughout the world is very popular for its unique quality, since its introduction.

Ceylon tea won such an accolade, due to its unique flavour, especially coming from regions like Dimbula (Talawakele – Hatton), Nuwara Eliya, Uva, Udapussellawa, Bogawantalawa and Maskeliya. Interestingly, apart from soil conditions and the terrain in which the tea is grown, climatic conditions prevailing in these regions contributed significantly, towards the development of such flavour compounds in tea leaf.

Since early 1990s, the leafy grade teas produced, mainly in the Low country (elevations <>

The leafy grade teas too are considered somewhat unique to Sri Lanka. But, Vietnam producing similar type of teas since of late, might pose a threat to the domination of Sri Lankan leafy grade type teas, had enjoyed for quite sometime, in the international arena.

Impact of global warming on productivity of tea at different elevations;

Up country:

Along with good soil conditions, well distributed rainfall and humid conditions, a mean ambient temperature of 20 – 26 0C has been identified as conducive for growth of tea. Tea is a rain fed crop, hence well distributed rainfall enhances its productivity. With global warming, the rainfall patterns have changed and the tea sector is already experiencing erratic weather conditions (higher rainfall during a shorter period of time and long spells of dry weather), which affect the overall productivity. Furthermore, such higher intensity rainfall also results in soil erosion, leading to low land productivity and hence crop losses.

According to data collected so far, the mean ambient temperature is about 14 – 23 0C, in the Up country. While low temperatures had been helpful in maintaining a higher organic matter content in the Up country, the ambient temperature is not the ideal for growth of tea. Thus, on one hand, due to global warming, the productivity in Up country is predicted to increase, with ambient temperature approaching the ideal, 20 – 26 0C.

On the other hand, with the elevation of temperature, some of the tea pests such as, shot hole borer, which were hitherto confined to low elevations, are seen to affect the productivity of tea plantations in Up country. Furthermore, crop losses are also predicted, due to increased activity of dry weather pests, such as Tea Tortrix, Mites etc., with rise in temperature.

Mid Country:

Although the mean ambient temperature in Mid Country 20 - 240 C, is somewhat ideal for growth, the low productivity recorded at present, could be attributed mainly due to eroded soils. With increase in temperature due to global warming, the soil carbon levels would further go down, due to increased carbon mineralization and it will further aggravate the lowering of soil productivity leading to more crop losses.

Low Country:

The mean ambient temperature in Low Country, 23 - 330 C, is already not only higher than the optimum, but it is close to the critical temperature (300 C), for growth. Thus, further rise in temperature will result in, lower productivity due to faster depletion of organic matter and also higher percentage of casualties too.

Impact of Global warming on quality of tea produced

The important reason for flavour development in tea leaf is, the climatic condition experienced in those regions. Although such conditions prevail through out the year, especially during a particular period of the year, the flavour is more pronounced. During the latter periods, the days are dry and the nights are cold, causing stress conditions to the plant, which in turn enhances flavour. Such climatic conditions exist in Dimbula, Bogawantalawa, Maskeliya and Nuwara Eliya during the period of November to February and in Uva as well as Uda Pussellawa, from July to September.

Increase in ambient temperature due to global warming is expected, to increase the night temperatures as well and hence would expose the tea plant to less stress conditions. Thus, a decline in overall quality (flavour) could be expected, in Up country.

However, the global warming might not lead to significant changes in quality of tea produced either in Low Country or Mid Country, provided that the leaf standard is maintained, at a satisfactory level.

Measures to mitigate the effect of global warming on tea production:

By establishment and management of shade in tea plantations, it is possible to mitigate the impact of rise in ambient temperatures in tea plantations. By having a good cover of high and medium shade, not only the mean ambient temperatures could be controlled, but soil fertility could also be improved, through leaf litter from those trees, in addition to lopping them as green manure at regular intervals. In the absence of such shade management, the option available is the installation of expensive irrigation systems, such as drip and sprinkler. However, considering the number of plants per unit area of land and the cultural operations involved (such as plucking every week), drip irrigation systems, might be difficult to maintain, where as the sprinkler systems should work. Furthermore, finding sources of water itself, to irrigate will be an issue during dry periods, under the global warming scenario.

Impact on the small holder sector:

With global warming, the small holder sector contributing, nearly 70% of the island’s production might, become vulnerable with regard to its productivity, as it is concentrated mainly in the Low Country. In addition to the effects of global warming, the adoption of short cut methods in tea cultivation practices, as a result of lack of know-how in this sector, might aggravate the situation. Under such a scenario, the contribution from Low country, which presently stands at 58 – 60% of the total, might decline.

Such a drop in production from the small holder sector will lead to, severe competition for green leaf, between private factories processing bought leaf. Thus, it will be prudent for the state to intervene and stop opening up of new factories, in Low country. If not, it will aggravate the unhealthy competition for green leaf already experienced in Low country, which in turn will lead to difficulties in maintaining the quality standards, established over the last so many decades, with great effort by the tea community.

It is hoped that overall wishful thinking and timely intervention by the sector as well as the state, would save this important industry and thereby sustain the image of Ceylon tea in the international arena!!!

(The author was the Director, Tea Research Institute, during the period 2003 -2006)

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