No abstract

Fertilizer is applied widely to improve the productivity of plantations. Traditionally, fertilization is conducted in spring and/or in the early rainy season, and it is believed to support the growth of planted trees in the growing season. Little attention to date has been paid on identification of the optimal timing of fertilization and fertilizer dose. In this study, application of the fine root monitoring technique in identifying optimal fertilization timing for an Acacia plantation in Vietnam is described. The study used two fertilizer doses (100 and 200 g NPK/tree) and three fertilization timings (in spring; in the early rainy season; and based on the fine root monitoring technique to identify when the fine roots reach their growth peak). As expected fertilization timings significantly affected growth and above-ground biomass (AGB) of the plantation. Fertilization based on the fine root monitoring technique resulted in the highest growths and AGB, followed by fertilization in the early rainy season and then in spring. Applying fertilizer at 200 g NPK/tree based on the fine root monitoring technique increased diameter at breast height (DBH) by 16%, stem height by 8%, crown diameter (Dc) by 16%, and AGB by 40% as compared to early rainy season fertilization. Increases of 32% DBH, 23% stem height, 44% Dc, and 87% AGB were found in fertilization based on fine root monitoring technique compared to spring fertilization. This study concluded that forest growers should use the fine root monitoring technique to identify optimal fertilization timing for higher productivity.

Acacia plantations have been contributing to national economic and livelihood of millions people living in rural areas of Vietnam. It has been widely planted and accounted for nearly 50% areas of plantations in Vietnam. In this study, different planting densities including 1,110 trees ha -1 (3 × 3 m), 1,330 trees ha -1 (2.5 × 3 m), and 1,660 trees ha -1 (2.5 × 2.5 m) were tested for Acacia hybrid and Acacia auriculiformis. The growth parameters (diameter at breath height/DBH and stem height/H) were measured, and dry biomass was estimated for 4-year-old plantations. The results indicated that a 4-year-old plantation of A. hybrid had most massive DBH (11.3 cm) at planting density of 1,100 tree ha -1 , while highest dry biomass (57.9 Mg ha -1 ) was observed in planting density of 1,660 trees ha -1 . In case of a 4-year-old plantation of A. auriculiformis, highest DBH (10.0 cm) and highest dry biomass (50.4 Mg ha -1) at planting density of 1,330 trees ha -1 were recorded. At the planting densities of 1,110 trees ha -1 and 1,660 trees ha -1 , a 4-year-old plantation of A. hybrid had Original Research Article

Background: Anoectochilus orchids have been widely used as medicine. However, it has been overharvested in nature because of high commercial values. This study aims at identifying distribution ranges and ecological characteristics of Anoectochilus orchids serving for sustainable development and describing traditional uses by ethnic people in Lai Chau Province, North Vietnam. Methods: Twenty-one plots of 100 m2 each (10 m × 10 m) were established for ecological survey and stand structures were analyzed for vegetation characteristics. While interviewing was applied to gather information on harvesting method, marketing, and medicinal uses. Results: Three Anoectochilus orchids (A. lanceolatus, A. calcareus, and A. setaceus) were found in Lai Chau Province, North Vietnam. These species distribute in both evergreen old-growth and secondary broadleaved forests, and mixed broadleaf-bamboo forest on the elevations of 996–2,134 m. They grow in forests with a high canopy cover of 67 m2 canopy area/ 100 m2 land and high cover (> 90% land) of low vegetation (< 2 m tall). It is believed that using the whole plant of Anoectochilus can treat hypertension and diabetes mellitus and improve the development of underdeveloped children. The folk uses include soaking in alcohol and boiled water for daily drinks like green tea, and consuming as a vegetable. The best harvesting season is during Autumn–Winter and fresh product is mainly marketed with the price of up to 100 U$D/1 kg fresh mass. Conclusion: A. lanceolatus, A. calcareus and A. setaceus are potential forest herbs for poverty reduction to ethnic communities in North Vietnam. The natural populations have been reduced remarkably because of overharvesting. Growing techniques are an urgent need for the conservation and sustainable development of such valuable orchids.

UDC 517.9The purpose of this paper is to investigate the Tikhonov regularization method for solving a system of ill-posed equilibrium problems in Banach spaces with a posteriori regularization-parameter choice. An application to convex minimization problems with coupled constraints is also given.