Assessing the suitability of bio - Climate conditions of phu tho province for the growth and distribution of tea

JOURNAL OF SCIENCE OF HNUE Natural Sci., 2008, Vol. 53, N ◦ . 5, pp. 161-170 ASSESSING THE SUITABILITY OF BIO-CLIMATE CONDITIONS OF PHU THO PROVINCE FOR THE GROWTH AND DISTRIBUTION OF TEA Dang Thi Hue Hanoi National University of Education Abstract. In this article, by analyzing bio-climatic characteristics of Phu Tho Province and comparing tea plant eco-biological requirements, the adaptability assessment of bioclimatic conditions of Phu Tho has been made. The result of the assessment shows that: Very suitable bio-climates: IA1a, IB1a, IIA2a and IIB2a, these areas are lower than 540 m, belonging to Ha Hoa, Thanh Son Phu Ninh, Lam Thao, Thanh Ba, Tam Nong, Thanh Thuy, Song Thao, Yen Lap, west of Doan Hung districts and Phu Tho township; Relatively suitable are IB1b, IIIA3a bio-climates; these areas are lower 600 m in Thanh Son district - western and southwestern parts of the province; Less suitable are IC1b, IVA4a bio-climates. It is very dry or mountainous - like Luoi Hai (> 900 m), Mountains Ten, Cam, Cam Co (> 700 m) in Thanh Ba district, because of the cold temperature regime, more than 5 cold months, tea planting isn't appropriate to the territory. 1. Introduction Phu Tho is a province located in the centre of the Northern Mountainous Region of Vietnam. It is famous for Hung King's ancestral land and is a long- standing native land for tea. The province is situated between 21 o 43' and 20 o 55' North Latitudes, 104 o 48' and 105 o 27' East Longitude. Its total natural area is 3,465 km 2 . Topography is relatively diverse including low mountains, hills and valleys; the highest is Luoi Hai Mountain (1,058 m). The topography is characterized by low mountainous and hilly ranges that originated from large denuded peneplain surfaces and composed of degenerate minerals. Phu Tho is also a meeting-place of Red, Da, Lo and many other rivers in the Red River system. Phu Tho belongs to the Northern climate region, has a monsoon tropical climate regime with cold winters. It is specified as a transition from plain to moun- tainous climates. 9 out of 10 districts of the province specialize in growing tea. The province is ranked first in national tea productivity and yield. The tea product of Phu Tho is not 161 Dang Thi Hue only a supply for domestic demand, but also a high quality product for exportation. Trade name of Phu Tho tea has been acknowledged in Europe and many other countries around the world. In 2007, the province grew nearly 14,000 ha of tea, yielded 7.4 tones/ha, produced more than 80,000 tones of fresh tea buds. Many factors influence the growth of tea, including soil, water, climate, hu- man beings, etc., of which, climate is one of the most important conditions having significant influence to the survival, growth and yield of tea. This paper analyses bio-climate characteristics of Phu Tho province, especially heat - humidity regimes, and assesses the suitability of those bio-climate characteristics for the growth of tea. 2. Content 2.1. Bio-climate characteristics of Phu Tho province 2.1.1. Radiation, cloud, sunlight and wind regimes Phu Tho has a relatively high radiation and sunlight regime that is good for photosynthesis of plants. Annual radiation is 118.9 Kcal/cm 2 /year. Annual sunlight is average with 1,580 hours/year. Overall cloud is average with 7.8 - 8.0/10 of fir- mament. In Northern and North-Eastern areas of Phu Tho where terrain is low and relatively flat, wind velocity is normally strong, annual wind velocity is 1.6 - 1.8 m/s. In mountainous and hilly areas in the West and the South-West of the province, annual wind velocity is gradually reduced to 0.7 m/s. 2.1.2. Temperature regime Temperature is an important ecological factor for the life of plants, and has a deep influence on the growth of plants. Crop plants live in suitable temperature conditions will grow well, producing high yields and good quality teas. Otherwise, if temperature is too low in winter or too high in summer, then it causes certain adverse impacts on plants. The temperature in Phu Tho is relatively high, about 22 - 23 o C annually, and clearly differentiated by topographical altitude. Most of the province's territory (about > 60% province's area) is under 160 m altitude with annual temperatures higher than 22 o C. In the Western and Southern areas of the province, temperature is gradually reduced with altitude: from 160 m to 540 m altitude, annual temperature is varied from 22 o C to 20 o C; from 540 m to 900 m altitude are mountainous areas, annual temperature is reduced, and varied from 20 o C to 18 o C. Above 900 m altitude are Western and South-Western Mountainous areas of the province (make up a small proportion and are located between Son La and Hoa Binh provinces), annual temperature is under 18 o C. Due to the influence of the winter's monsoon wind, temperature regime in Phu Tho makes for 2 clear seasons: hot and cold. The hot season (the period with a monthly temperature higher than 25 o C) lasts 162 Assessing the suitability of bio-climate conditions of Phu Tho province... about 5 months, from May to the end of September. July is the hottest month with a monthly temperature of about 33.1 o C. The cold season (with monthly temperatures lower than 18 o C) is about 3 months, from December to February of the year after. January is the coldest month with monthly temperatures around 15.7 - 16.2 o C. 2.1.3. Rain and humid regimes a. Rain regime Plants can not survive without water. Water makes up 40 - 90% of a plant's component. Water is needed for photosynthesis, respiratory, growth, and bio-chemico- phisical process of plants. In Phu Tho, annual rainfall (R year ) is differentiated and increased gradually from East to West and from low to high areas. Annual rainfall in the province is at medium level (1,500 - 2,000 mm) compared to many other places. The lowest annual rainfall is 1,545 mm in North-Eastern area of the province (Doan Hung district), and the highest annual rainfall reaching 1,997 mm in North-Western area of the province (Am Thuong commune) [1]. The rainy season in Phu Tho is summer. The rainy season (with monthly rainfalls higher than 100 mm) is 7 months, starting in April and ending at the end of October. The low rain season lasts 5 months, starting in November and ending at the end of March of the following year. b. Humid regime High or low air humidity influences the water balance between plants and the environment. High humidity constrains water evaporation; low humidity causes strong water evaporation from plants, the water taken from plant's root may not be enough to compensate for evaporation, thus, tension of plant's tissues is reduced leading to dry plants. Air humidity in Phu Tho is relatively high and equally distributed around the year. Annual humidity is higher than 81%. The annual lowest humidity is about 60 - 62%. Winter is a relatively dry period; lowest humidity is reduced to 57 - 59%. In Viet Tri, humidity in the first months of winter is reduced to 57%. 2.1.4. Unusual weather Unusual weather such as dry and hot wind, hoarfrost, hurricanes, tropical low pressure, hail, storms, etc. occurred at low frequency (sometimes once a year); however they cause serious impact on plant life and their yield. a. Mist: mist is relatively common in Phu Tho, however the number of misty days is not equal in places. In Phu Ho, the number of misty days is relatively high, nearly 50 days per year; mist occurs nearly every month, averaging 1.5 days per month, highest 6.6 - 8.3 days per month at the end of autumn and beginning of winter. In other locations such as Viet Tri and Minh Dai, the number of misty days is low, on average 6 - 8 days per year. b. Hoarfrost: hoarfrost is rare in the low areas of Phu Tho. In the West 163 Dang Thi Hue and South-Western Mountainous areas, it occurs in December and January with low frequency. c. Drizzle: drizzle is scattered in October, November, and December (about 0.04 - 2.7 days/month). Number of drizzly days clearly increases in January, averag- ing 3.5 - 6.3 days/month. Highest drizzle occurs in cold and humid months: January and February for 5 - 6 days/month. In April, the number of drizzly days is reduced to 4.2 - 4.7 days/month and in June, drizzle is rare. d. Hail: hail occurs with low frequency in Phu Tho, however it has a bad impact on agricultural production; therefore, this type of unusual weather should be paid adequate attention. According to statistic data for many years, the number of hail days in the province is 0.1 - 0.4 days/year. e. Storms: storms occur in about 60 days/year. Early storms start at the end of February and beginning of March with low frequency (2.1 - 3.3 days/month). From April, the number of days having storms is increased significantly (averagely 6.7 days), thus April is considered as the beginning of the storm season. In the storm season, the number of days having storms increases from month to month and reaching maximum in July (12.5 days). Also, the number of days having storms is gradually increased from plain areas to Western and Southern Mountainous areas of the province. f. Dry and hot wind: is a special weather phenomena occuring in summer months with a combination of typical weather such as: Western wind rapid of 2 - 3 m/s, temperature T 13o'clock ≥ 35oC, humidity U 13o'clock ≤ 65%. In Phu Tho, number of days having dry and hot wind is not high, averaging 18 days, 12 - 18 days/year in areas located at around 200 m altitude, and 0 day in areas from 500 m altitude and above. 2.2. Assessing the suitability of bio-climate conditions for tea in Phu Tho province 2.2.1. Map assessing the suitability of bio-climate conditions of Phu Tho province for tea Analyzing the impact of the temperature-humidity factor to the growth of tea, and the ecological characteristic of tea, we propose a set of bio-climate criteria to assess the suitability of the territory's conditions for tea as follows: Temperature criteria: based on monitoring data gathered for several years from Phu Tho's weather stations, and data gathered from nearby areas (Thai Nguyen, Vinh Phuc, Bac Kan, etc.), we classify the temperature of Phu Tho province (annual temperature Tn«m ) into 4 levels: - I: rather hot, T year ≥ 22oC, total temperature/year ≥ 8,000oC, distributed in areas at ≤ 160 m altitude. - II: warm, T year = 20 o C - 22 o C, total temperature/year from 7,300 - 8,000 o C, distributed in areas from 160 m to 540 m altitude. 164 Assessing the suitability of bio-climate conditions of Phu Tho province... - III: cool, T year = 18 - 20 o C, total temperature/year from 6,500 - 7,300 o C, distributed in areas from 540 m to 900 m altitude. - IV: rather cold, T year < 18 o C, total temperature/year < 6,500 o C, distributed in areas above 900 m altitude. Criteria on length of cold season: as many other places in the North, the frequency occurrence of low temperature period (< 18 o C) in Phu Tho has certain influence on the growth of crops in general and of tea in particular. That low tem- perature period is classified based on number of cold month in year (is marked as N) into 4 levels as follows: - Level 1: rather short winter, number of cold month in year N < 3; - Level 2: short winter, N = 3 - 4; - Level 3: average winter, N = 4 - 5; - Level 4: long winter, N > 5. Humidity criteria: Analyzing the spatial distribution of annual rainfalls, we find that annual rainfall in Phu Tho can be classified into 3 levels: - A: Heavy rain, R year ≥ 1,800 mm; - B: Average rain, R year = 1,600 - 1,800 mm; - C: Low rain, R year < 1,600 mm. Criteria on length of dry season: the dry season in Phu Tho is not clearly differentiated, averaging 3 - 4 months (monthly rainfall ≤ 50 mm), of which, 1 - 2 are drought months (monthly rainfall ≤ 25 mm) and no exhausted month (monthly rainfall ≈ 5 mm). Length of dry season in Phu Tho can be displayed by the number of dry months (is marked as n). Dry season in Phu Tho can be classified into 2 levels: - Level a: average dry season, number of dry month n = 3 - 4; - Level b: long dry season, number of dry month n ≥ 5. Based on the integration of all above temperature-humidity criteria, map as- sessing the suitability of bio-climate conditions for tea in Phu Tho is established (Figure 1). The map presents 8 bio-climate units with different suitability levels for tea, includes: IA1a, IB1a, IB1b, IC1b, IIA2a, IIB2a, IIIA3a and IVA4a. 2.2.2. Assessing the suitability of bio-climate conditions of Phu Tho province for tea - Suitability of temperature regime: Research results on ecological conditions for tea shows that the higher am- plitude of temperature between months, the shorter time is needed for picking tea leaves; on the contrary, the lower amplitude of temperature between months, the longer time is needed for picking tea leaves. In Phu Ho tea farm, tea buds appear and start a strong growing period by 20 February (earliest on 5 February, latest on 6 March), after a short winter break. Monitoring data gathered for several years shows that the growth period for spring tea crop is closely related to the day that 165 Dang Thi Hue air temperature exceeds 15 o C. In Phu Ho, there are 6 - 8 tea grow periods/year, averaging 7 periods. Tea buds are grown in 2 main periods: germination of tea buds from sleeping and formation of tea buds. The germination of tea buds for picking results from stimuli: buds are con- verted from sleeping to active. The sleeping period normally take a long time in conditions of low temperature and rainfall and it takes less time in convenience con- ditions of high temperature and rainfall. Effective temperatures in this period varied from 22 o C to 28 o C, depending on tea varieties. High temperature promotes biologi- cal processes, nutrient and stimuli accumulation, and facilitates the germination and growth of sleeping buds. The formulation of tea buds are started from appearance to maturity of tea buds. This is a very important period due to related formulation of buds, yield and quality of tea. The relationship between the period of time for formulation of tea buds and average temperature shows that average air temperature of 18 - 24 o C is a good condition to form tea buds; 24 - 28 o C is a less convenience condition to form tea buds; at temperatures higher than 30 o C, the growth of tea buds will slow down; and at 40 o C, young parts of tea will be come grey. Based on the ecological needs at different growth periods of tea (period for germination of tea buds, period for formulation of tea buds, etc.), the existing dis- tribution of tea in the province, and the differentiation of temperature in Phu Tho, we integrate and present assessment results as 3 main levels: suitable, relatively suitable, and less suitable (Table 1). Table 1. Assessment results on suitability of temperature for tea Symbol Temperature Suitability I1 Rather hot, rather short winter Very suitable II2 Warm , short winter Very suitable III3 Cool, average winter Relatively suitable IV4 Rather cold, long winter Less suitable - Suitability of rain and humid regime: Rainfall has a considerable effect on the growth of tea. According to reference [1], every 0.405 ha tea available for picking buds will consume nearly 10 tonnes of water/day (which is comparable with 2.54 mm of rainfall/day). Thus, if rainfall is distributed evenly to minimize water loss from surface run-off and evaporation, then minimum water is needed for water evaporation from tea leaves is 1143 mm/year. Drizzle also plays a certain role in the growth and yield of tea in Phu Tho midland, at the same time it facilitates the growth and spread of insects. Rainfall from drizzle is low, however distributed evenly, it helps to increase air humidity that is good for the growth of tea buds. In Phu Tho, rainfall in January, February and 166 Assessing the suitability of bio-climate conditions of Phu Tho province... March is low but the number of drizzly days is about 20 days/month, therefore, in warm weather tea can still germinate and grow buds normally. Tea in Phu Tho has two growing periods: the first one is in March called spring tea; the second one is called summer-autumn tea. The effect of temperature-humid conditions on tea yield is different for these two periods: Spring tea: After a short winter break, tea will start to grow again in conve- nience weather. In general, spring tea output is not high (makes up 10 - 13% yearly output); tea buds are stout, leaves are big and soft. Spring tea has high yield in years which have humid winters and warm springs, and relatively low yields in years with dry winters and cold springs. Summer-autumn tea: from May, when the temperature is a convenience factor, yield of tea will depend on the humidity factor or rainfall in these months. Also from May, tea yields are gradually increased, maximum in August, September, then, tea yields are gradually reduced and stop producing buds at the end of November. Monthly summer-autumn tea output varies in accordance to annual rainfall. In Phu Ho tea farm, tea output exceeds 10% in months with rainfall higher 100 mm/month (March, April), and tea output is less than 5% in months with rainfalls lower than 50 mm/month (November, December). Based on differentiation of rainfall in Phu Tho, ecological needs of tea, existing distribution of tea in Phu Tho province, we find that rainfall and humidity in Phu Tho create different conditions for tea. Results of assessment are classified in three levels: very suitable, relatively suitable, less suitable (Table 2). Table 2. Results from assessing the suitability of rain-humid regime for tea Symbol Rain-humid characteristics Suitability Aa High rain, average dry season Very Suitable Ba Average rain, average dry season Very Suitable Bb Average rain, long dry season Relatively suitable Cb Low rain, long dry season Less suitable - Effects of unusual weathers: Drought, dry and hot of west wind effects the growth and reduce the yield of tea. The most concerning is wind and high temperature and low humidity lasting for a long time. It is observed that in the first days of dry and hot winds, (temperature > 35 o C, humidity < 55%), young tea buds are wilted; medium and old leaves are converted from fresh to be soft, doughy and grey. In second day of dry and hot winds, tea is aggrieved, dried, and stops growing in height. The longer the time of dry and hot winds the more serious impact. Therefore, in areas where dry and hot wind occurs, tea should be prevented by forest barrier or tree growth; if available, soil should be covered to maintain humidity and tea should be watered. Hoarfrost also has a bad impact on young tea buds. Hoarfrost combined with 167 Dang Thi Hue low temperatures (under 0 o C) and lasts for many days will cause damage to the tea. In Phu Tho, hoarfrost normally occurs in December and January; attention should be paid to protect tea from it. Especially, San Tea is a variety growing in the mountains, it grows well in cold and hoarfrost conditions (it is normally planted in high terrain). Every year teas are cut down, therefore teas are less impacted by storms and hurricanes. Integrating assessment results on annual temperature, number of cold months, annual rainfall, length of dry season, taking into account unusual weather, then presenting all on map assessing the suitability of bio-climate conditions of Phu Tho province for tea, we identify areas for growing tea at three levels: very suitable, relatively suitable, less suitable (Table 3). Table 3. Integrating the suitability of bio-climate conditions in Phu Tho for tea Symbol Level of suitability Distribution IA1a All Ha Hoa district; Song Thao district; West and East of Thanh Ba district; East, North-East and the Southest point of Yen Lap district; West, South of Doan Hung IB1a Very suitable district, North of Phu Ninh district, all Phu Tho town, two districts Tam Nong and Thanh Thuy, nearly all Thanh IIA2a Son district (accept low mountainous and hill areas higher 540 m). IIB2a IB1b All Viet Tri city, Lam Thao district, half of West of Phu Ninh district. IIIA3a Relatively suitable Low mountainous and hill areas in West and South West of the province; include Tu Tinh Mountainous area (higher 700 m altitude) in the South-East, Cam Co Moun- tainous area in the North-East, Luoi Hai Mountainous area in the East of Thanh Son district and mountainous area in the Southern margin of Thanh Son district, at 540 m altitude. Gioc Mountainous area, Doi Muong in the North of Thanh Son district, in the East of Yen Lap district, etc... IC1b Small part in the North of Doan Hung district. IVA4a Less suitable Scattered distribution in some high mountainous areas such as Luoi Hai Mountainous area (higher than 900 m altitude), Ten, Can, Cam Co Mountainous areas (higher than 700 m) of Thanh Son district, etc... 168 Assessing the suitability of bio-climate conditions of Phu Tho province... Figure 1. Map assessing the suitability of bio-climate conditions of Phu Tho province for tea Legend: Very suitable: IA1a, IB1a, IIA2a, IIB2a; Relatively suitable: IB1b, IIIA3a; Less suitable: IC1b, IVA4a. 169 Dang Thi Hue 3. Conclusion Map assessing the suitability of bio-climate conditions of Phu Tho Province for tea is established based on analyzing the bio-climate conditions of Phu Tho and comparing ecological needs (temperature, humidity) of tea with bio-climate conditions (temperature, humidity) of Phu Tho. Assessment results presented in map (Figure 1) show that many areas in Phu Tho are bio-climately suitable for the growth of tea. Very suitable for tea: are bio-climate units IA1a, IB1a, IIA2a and IIB2a. These are low hill areas (lower 540 m altitude) in Ha Hoa, Thanh Son, Phu Ninh, Lam Thao, Thanh Ba, Tam Nong, Thanh Thuy, Song Thao, Yen Lap districts, west of Doan Hung district and Phu Tho town. Relatively suitable for tea: are bio-climate units IB1b, IIIA3a. These areas are lower 600 m areas, distributed in Western and South-Western areas of the province, mainly belonged to Thanh Son district. Areas from 600 m and higher, where the cold season is approx. 4 months with average temperatures of < 18 o C, and rainfall is high (≥ 1800 mm), are suitable for San Tea variety which can grow well in cold climates and provide strong flavors. However, these areas are relatively small, scattered in high mountainous areas of Thanh Son district. In general, San tea variety is less developed here with a low yield and taken less care as well no investment. Less suitable for tea: are bio-climate units IC1b, IVA4a. These are low rainfall, drought areas or high mountainous areas such as: Luoi Hai Mountainous area (higher 900 m), Ten, Can, Cam Co Mountainous areas (higher 700 m) of Thanh Son district, etc. Due to low temperatures, 5 months of cold season, high rainfall≥ 1800 mm/year, these areas are less suitable for tea. In practice, tea in these areas is a low yield due to hard temperature-humidity conditions. REFERENCES [1] Le Tat Khuong, 1999. Tea manual. Agricultural Publishing House, Hanoi, (in Vietnamese). [2] Vu Tu Lap, 1999. Physical geography of Vietnam. Education Publishing House, Hanoi, (in Vietnamese). [3] Nguyen Khanh Van, 1990. Effects of climate conditions on characteristics of agricultural ecosystems (Vinh Phu midland) from human ecology approach. Geog- raphy  Natural Resource Unit, Vietnam National Centre for Scientific Researches, (in Vietnamese). 170