Assessing climate and soil conditions to grow mandarin trees in Bac Son district, Lang Son province

HNUE JOURNAL OF SCIENCE DOI: 10.18173/2354-1067.2017-0051 Social Sci., 2017, Vol. 62, Iss. 5, pp. 194-200 This paper is available online at ASSESSING CLIMATE AND SOIL CONDITIONS TO GROW MANDARIN TREES IN BAC SON DISTRICT, LANG SON PROVINCE Bui Thi Thanh Dung Faculty of Geography, Hanoi National University of Education Abstract. Lang Son is one of the few localities of Vietnam that has favourable local climate and soil conditions to grow yellow mandarin trees. The context of typical tropical monsoon climate in mountainous area and soil characteristics, especially types of feralit soil, have quite suited to the ecological characteristics of mandarin trees. Mandarins in Bac Son district (Lang Son provice) is always known for agricultural specialty and high quality product. This has been long considered as a key crop in poverty reduction and improvement of local people’s living standards. Keywords:Mandarin trees, mountainous climate, feralite soil, adaptive assessment. 1. Introduction Bac Son district in Lang Son province is a rural district in the Northeastern region of Vietnam. The district covers an area of 679,9 km2 in which forests and mountains accounts for majority of the total area. The main crops in the dictrict are rice, maize, industrial trees, fruit, livestocks. . . Growing mandarin trees is in favor of farm households in Bac Son district. Mandarins are tropical fruit with sweet flavor and creamy texture and well-known for their high nutrious value and the economic efficiency. In recent years, the growth of mandarin oranges in Bac Son has become main sources of income for a considerable number of housholds in the district, which helps the local people in the district reduce poverty and increase their living standards. Bac Son district has favorable conditions for growing mandarin trees in large quantity. The area of cultivated land for this type of fruit has increased in recent years. To protect and develop the precious variety of mandarins in Bac Son, the need for assessing natural conditions for this specilaty agricultural product has highly increased. Due to the of the important role of mandarins and acknowleging the favorable conditions for growing mandarin trees in Bac Son district, the aim of this study, therefore, is “Assessing climate and soil conditions to grow mandarin trees in Bac Son district, Lang Son province”. Received date: 7/12/2016. Published date: 5/5/2017. Contact: Bui Thi Thanh Dung, e-mail: buithanhdung83@gmail.com 194 Assessing climate and soil conditions to grow mandarin trees in Bac Son district... 2. Content 2.1. Ecological characteristics of mandarin trees Trees vary in individual size and sweetness of their fruit. And, some trees may be more resistant to diseases. Naturally, mandarin growers, to ensure the best possible crop, want to make sure all their trees are of the same high quality. To do this, each new tree they plant is grown, or propagated, not from a seed but by grafting or budding. In most mandarin trees, the scion, or top of the tree, is a different variety from the roots or rootstock of the tree. Temperature: mandarin trees grow and develop well at the temperature of 12-390C, preferably at the temperature of 25-270C. When the temperature is below 50C or over 400C, the trees stop growing. Large temperature amplitude can promote fruit’s growth, stimulate the accumulation of sugar, flour, organic acids of the fruit and enhance ripening and beautifying color skin. Pruning: unlike most other fruit trees, mandarin trees don’t require regular pruning. Commercial growers trim tree tops to keep them smaller so they are easier, safer and less expensive to pick, and "hedge" the sides to let more sunlight into the trees to improve yields. Hand pruning opens up the trees to allow more sunlight into the center. Soil type: mandarin will grow in most soils from sandy to adobe clay, provided it drains well. Sandy soils must be watered and fertilized more frequently than soils with a higher clay content and growers can add organic matter such as manure or compost to improve water and nutrient holding abilities. Mandarin trees can grow and thrive in the condition of loamy and breathable soil, with thick soil layer, good moisture, good drainage, low underground water. Do not plant mandarin trees on heavy clay, sand or old sand soil, laterite soil or high underground water and poor drainage. The suitable pH for growing well mandarin trees is 5.5-6. Irrigating and fertilizing: water quality is very important. Water high in salt content, common in some desert regions, can cause injury to leaves, burning leaf tips and margins. Lower levels of salts can cause the tree to grow poorly or to produce fewer or smaller fruit. Nutrients that mandarin needs in relatively large amounts are nitrogen, phosphorous, potassium, sulfur and calcium. In lesser amounts, citrus requires iron, magnesium, copper, zinc, manganese, molybdenum, boron and chlorine. Mandarin trees prefer moisture and low drought-resistance but can not grow in the waterlogged condition. Approprivate rainfall for mandarin plantation is 1500-2000mm/year, soil moisture of 60% and air humidity makes the fruit ripen faster and produces good quality, beautiful skin. 2.2. Natural conditions and ecological adaptive assessment of improving mandarin trees in Bac Son district, Lang Son province Bac Son district is a mountainous area in Lang Son province. It has a natural land area of 69,786 ha, 40% of which is rocky and hilly. The total population is 66,100 people (2012), population density is not evenly distributed. The district has 19 communes and 1 town. In general, Bac Son is a mountainous district but located in a favorable geographical location for socio-economic development. 195 Bui Thi Thanh Dung 2.2.1. Climate and weather Bac Son is located in the north east of Vietnam therefore it is influenced by tropical monsoon climate of the mountainous areas. According to the meteorological statistics, the average annual rainfall is estimated 1500-1600mm, 1780mm is the highest rainfall in June, July and August. The lowest rainfall is 912mm, in December and January. The humidity is 82%. Compared with districts in Lang Son, Bac Son often has lower rainfall. It is difficult condition for the development of plants and animals. The average temperature all year is 20.80C, the highest temperature in June is 26.80C, January and February have the lowest temperature of 13.80C. The radiation is quite low in comparison with tropical climate areas, the average number of sunshine hours a year is 1729 hours, the average hours per day is 4.4 hours. Such radiation characteristics can be favorable conditions for developing some typical plants. The average air humidity is 81%, the highest 85% and lowest 72%. Located in limestone Acre, Bac Son is not directly affected by the wind storms. Climate and weather create suitable conditions for the development of mandarin trees, but there are certain difficulties for developing mandarin trees as Bac Son has a cold winter, often influenced by the cold and damage weather . 2.2.2. The land Table 1. Land use over 3 years 2013-2015 in Bac Son District Types of land 2013 2014 2015 Development rate (%) area (ha) % area (ha) % area (ha) % 2010/ 2009 2011/ 2010 Total natural area 69.786 100 69.786 100 69.786 100 100 100 I. Agricultural land 11.671,54 16,72 11.652 16,7 11.631,51 16,66 99,83 99,82 1. Annual crop land 8.423,77 72,17 8.308,79 71,3 8.230,56 70,76 98,63 99,06 2. Land for perennial trees 1.934,42 16,57 2.047,76 17,57 2.106,24 18,1 105,86 102,85 3. Ponds 803,45 6,88 772,61 6,63 715,15 6,14 96,16 92,56 4. Other agricultural land 509,9 4,38 522,84 4,5 579,56 5 102,53 110,84 II. Non - agricultural land 29.057,46 41,64 29.307 42 29.548 42,34 100,85 100,82 III. Unused land 29.057 41,64 28.827 41,3 28.606,49 41 99,2 99,23 (Source: Department of Agriculture and Rural Development in Bac Son district) 196 Assessing climate and soil conditions to grow mandarin trees in Bac Son district... Land is an important resource because it covers about 30% of the total area of the earth’s surface and all parts of this small percentage are habitable or productive. All other resources are provided by land and it is on land that buildings and industries are made. Land is the home to many species of plants and animals,including humans,and so it is the most valuable natural resource. Bac Son district has a total land area is 69,786 ha, of which agricultural land accounts for 16.66% (11,631 ha of natural areas). Over the past 3 years, agricultural land per capita decreased by 0.17% per year, this is due to the fact that land is being transferred to building houses, rural construction planning... However, cultivation of fruit trees tends to increase. But agricultural land of the districtis limited, the policy of the district and people’s desire are to transfer a portion of land for less effective annual crops to land for growing fruit trees to increase the income. On territory of the district, there are 5 groups of land with 10 major soil types, including red and yellow soil on shale with the greatest area of 18653.5 ha, accounting for 26.7% of the natural area. Meanwhile the black soil takes up only 121.7 ha, accounting for 0.2% of the natural area. In terms of area of land slopes and thick layer, the majority of land in the district has thin layer, some thick layer area is located on the slope, therefore there is no possibility of agricultural production. The area which has slopes of below 150 and smooth soil of below 70cm is 14099.3 hectares, accounting for 35.17% and 20.20% of the natural land area. This area can be arranged to grow perennial crops including mandarin trees. The majority of the land area of Bac Son district has acidic reaction (pH <5). Natural fertility of the soil is very variable depending on many factors. The results of the appropriate land for mandarin trees showed that highly suitable land area is 570.5 hectares, quite appropriate land of 822.2 ha; less appropriate land of 15323.1 ha and unfavorable land for growing mandarin trees is 23300.7 ha. Land in Bac Son is suitable for growing crops such as mandarin oranges, pears, plums, apricots, corn, star-anise,... 2.2.3. Water resources With mountainous terrain, alternating between the relatively flat valley, in the district there are many lakes, rivers and streams scattered in almost every corner around the district. Local people’s damming water creats small reservoirs. In the district, there is Tam Hoa lake with a water surface area of 36 ha, and Vu Lang lake has a water surface area of 270 ha. This is very large surface water resources. To exploit the water supply, the district has multiple irrigation as: Ho Tam lake, Mo Pac lake, Tran Yen lake... and more than 40 pumping stations with more than 90 small dams. Table 2. Ecological adaptation of natural conditions for mandarin trees in Bac Son district (Lang Son province) Targets Symbol Value Unit Explanation Adaptive level Quite adaptable Medium Less None I. Group of heat – humidity indicators 1. Average temperature 1 <18 Cool + 2 18-20 Warm + 3 20-24 0C Abit hot + 4 24-27 Hot + 197 Bui Thi Thanh Dung 5 >27 So hot + 2.Average annual rainfall 1 <1.500 Little + 2 1.500-2.000 mm Medium + 3 2.000-2.200 Pretty much + 4 >2.200 Much + II. Group of physical and soil nutrition indicators P Slob + 3.Type of soil D Valley land due to condensed product + Fa Gray feralite soil on magma acid rock + Fs Gray feralite soil on clay + Hs Red-yellow muddy soil on clay + E Soil erosion in stone + 4.Soil layer thickness x <70 + y 70-100 cm + z >100 + 5. Mechanical components a Sand + b Sandy phase + c Light argil + d Medium argil + e Light clay + III.Group of terrain norms 1 <8 Flat + 6. Slope 2 8-15 degree Less sloping + 3 15-25 Sloping + 4 >25 Quite sloping + 7. Height 1 <200 m + 2 200-500 + 3 500-1000 + 4 >1000 + (Source: The results have been evaluated by the author) 198 Assessing climate and soil conditions to grow mandarin trees in Bac Son district... Currently it has been drilled for assessment of quantity and quality, but through the preliminary surveys, in the depth of wells is 20-25m then appear burst into groundwater, water quality is quite good. This is a very popular fruit in Bac Son because of its sweet flavor, small weight, ease of peeling and its easy-to-separate segments. Bac Son mandarins are small sweet oranges with a loose skin. They have a light orange color and a complex, sweet flavor. The classic mandarins in Bac Son offers a superior flavor and aroma. Mandarins grow mostly in Bac Son district, Lang son province, where the climate, soil and growing conditions are just right. On holiday occasions, people often buy mandarins as gifts for their friends and family. This special fruit is preferred because of its safety and special sweet flavor. 2.3. The scale of production, productivity and yield of mandarin trees 2.3.1. The scale of production Bac Son mandarin trees are considered one of the key crops of the district. In recent years, Bac Son mandarins production remained relatively stable in terms of area and production capacity. Table 3. Area, yield and production of Bac Son mandarins period 2013- 2015 Year Total area (ha) Harvesting area (ha) Productivity (100kilo/ha) Yield (ton) 2013 965.01 433,6 29,17 1264,9 2014 926,83 410,42 31,38 1288 2015 945,13 434,10 30 1302,4 (Source: Department of Agriculture and Rural Development in Bac Son district) In recent years, the area for growing mandarins continues to grow by planting new trees every year. The district in 2010 had only 678 hectares of mandarin oranges while in 2015, the total area was 945.13 ha. The ancient trees of hundreds of years old with extensive coverage nearby mountain valley of rocks which are rich in vegetation and moisture. But now these trees have been cut down, which leads to decrease of the humidity in the cultivating areas. In addition, another reason is the majority of mandarin growers still use extensive backward planting techniques. 2.3.2. Productivity and yield Mandarin trees are perennial, the yield depends not only on varieties, the level of investment and farming techniques, on the climatic conditions, but also on the age of the tree. Average of 4-5 years for the harvest to begin, the initial yield is about 30 to 40 kg/tree. At the age of 7 to 10 years, an average yield of 40 to 60kg/tree and gain the value of 600.000-1 million/tree. Nhat Hoa commune, Nhat Tien, Tan Lap commune have the highest number of mandarin trees of over 20-year-old in the district, many families have mandarin trees up to 40-50 years old. The average yield of mandarin trees is about 30 kg/ha. But the impact of the cold weather and winter damage, and prolonged drought in May, June’s in recent years have made significant impacts on productivity, yield of mandarins in the district which is only 199 Bui Thi Thanh Dung 31.38 kg/ha (2014) and 30 kg/ha (2015). Since 2010, Mandarin production has gone through strong fluctuations. Due to the adverse impact of favorable climate conditions, mandarin output of the district was 1264.9 tons in 2013 and 1288 tons in 2014. 3. Conclusion The terrain conditions in Bac Son district with topographical forms are hills, mountains, valleys. They are interspersed and divided complex. On the other hand, the differences in surface creates its own unique climate. The typical tropical monsoon climate in mountainous area and special soil conditions facilitate Lang Son province to become one of valuable mandarin plantation provinces in the northeastern region of Vietnam. REFERENCES [1] Bui Thi Thanh Dung, 2004. “The climate condition in Lang Son province”. Graduation Thesis, Hanoi. [2] “Data about mandarin trees in Bac Son district, Lang Son province”, Department of Agriculture in Lang Son province, 2015. [3] “Establishing and managing the rights to the geographical indications for mandarin products in Lang Son province”, Department of Science and Technology in Lang Son province, 2010. [4] “Reports on socio-ecoonomic development of Bac Son district, Lang Son province (2013-2015), Department of Agriculture in Lang Son province. [5] “Reports on agricultural achievements in 2014 and plans for 2015, Bac Son district”, Department of Agriculture in Lang Son province. 200