The custard apple from Lục Nam has long been known for its cool and sweet taste as well as its chewy texture. Custard apple has been cultivated in Lục Nam for a very long time. At first, it was treated as a treat of local families. In 1987 - 1988, many people found this custard apple tasty, so they started ordering the product. Lục Nam custard apple began to follow the merchants to further markets of other regions, especially in Hà Nội, Quảng Ninh, Vĩnh Phúc, Hải Phòng, Nghệ An, etc. Since the 1990s, Lục Nam farmers have begun to develop areas for custard apple. In the recent 15 years, custard apple has become the main economic force of the region. After decades of cultivating and tending the custard apple, Lục Nam farmers has discovered tasty custard apple variety, further honed their technique to increase the productivity. With the quality variety and excellent cultivation technique, Lục Nam custard apple has become the flagship product of Lục Nam farmers.
Lục Nam custard apple
Lục Nam has heart shape, lumpy green-yellow skin. The crevises are yellow-white. Fruit diameter is 74.31 – 89.68mm, fruit height is 68.66 – 85.84mm, and the weight is 299.56 – 466.40g per fruit. The edible percentage of Lục Nam custard apple is 54.20 – 66.75 %. When eaten, the custard apple has a faint aroma and cool and sweet taste with a hint of sourness and no acrid taste. These specific traits of Lục Nam custard apple are thanks to the high total sugar content and degree Brix (total sugar content: 12.05 – 12.56 %; degree Brix: 15.96 – 19.04 %), while the acidic and vitamin C content is lower than others (total acidic content: 1.61 – 1.90 %; vitamin C content: 36.79 – 43.38 mg/100g of fresh edible). Lục Nam custard apple also has an especially high Cellulose (fibre) content at 0.88 – 1.62 % of dry matter. Therefore, it benefits the digestive system of the consumer.
The peculiar characteristics of Lục Nam custard apple are thanks to the natural conditions of the geographical area. The area has the climatic traits of the Northeastern mountainous region. The rainy season is from April to September and the dry season is from October to March. The annual average temperature is 20 - 25°C. Annual average rainfall fluctuates between 895 to 2.988 mm per annum. Annual average humidity is 80 - 85%. Annual average total hour of sunlight is 1,401 hour. Annual average total evaporation is 750 - 850 mm. In general, the evaporation is lower than rainfall, combining with the system of rivers, streams and lakes for water reserve, so the drought during dry season does not happen regularly.
The geographical area is near the hills with the inclination of under 15°, the topography is that of the high mountains and low hills, highly suitable for applying technology to the production. As Lục Nam custard apple production area resides on the mountain base and low hills area, its taste is often sweeter than other custard apples cultivated on high limestone mountains. Lục Nam province has the Lục river flow by, the river banks are deposited with alluvium which is suitable to the development of custard apple trees. The soil of the geographical area consists of Oxisols and Leptosols. The mechanical composition is medium, clay and sandy silt. The soil has much acidic reactions, the pHH2O level of layer 1 is within the range of 4.4 – 5.4, pHKCl level of layer 1 is 3.80 – 4.60. The pH level of the production area of Lục Nam custard apple is entirely different to that of other custard apple areas, and highly compatible with the nature of custard apple (prefer acidic soils).
Aside from the natural conditions, the production, harvest and preservation technique of the local producers also contributes to the peculiarity of Lục Nam custard apple. After each harvest, Lục Nam custard apple producers will prune old trees, or branches inside the foliage for mature trees, combining with fertilising and tending so that the next harvest will have many big and quality fruits. The pruning also allows the flowers to bloom and the fruit to grow on the tree barks, avoids the impact of wind that can make fruits on branches to drop and crash. Moreover, Lục Nam is also the first area to discover and apply the technique of additional pollination to prolong the harvest season, and also prevent the fruit from ripen at the same time, leaving the farmer enough time to harvest. Additionally, the use of straw ash as fertilizer supplements Potassium which helps the bud splitting, lowers the rates of fruit dropping and improves the rate of fructification, enhances the quality of the product through the accumulation of sugar and vitamins, resulting in better appearance, taste and longer preservation. Therefore, Lục Nam custard apple has brighter colour and takes longer to darken than other custard apples.
The geographical area: The communes of Đông Hưng, Đông Phú, Cương Sơn, Lan Mẫu, Huyền Sơn, Nghĩa Phương of Lục Nam district, Bắc Giang province./.