Tropicultura (Jan 2009)
Utilisation agricole de plantes aquatiques, notamment en tant qu'amendement des sols, dans la province de Thua Thien Hue, Centre Vietnam. 2. Relevé des pratiques de terrain, enquête auprès des agriculteurs, impact potentiel sur l'écologie de la lagune de Tam Giang
Abstract
Use of Aquatic Plants, mainly as Soil Amendment, in the Thua Thien Hue Province, Central Vietnam. 2. Field Practices, Survey among Farmers, and Possible Impact on the Tam Giang Lagoon Ecology. The sandy soils of the coastal area of Central Vietnam, particularly in the Thua Thien Hue Province, have a limited natural fertility. Amending these soils with organic materials is the most important way to improve their productivity. In this region, numerous farmers are fertilizing their soils with aquatic plants collected from the Tam Giang lagoon. The present study aims to provide quantitative and qualitative data on this local practice, based on a survey among the farmers and on field observations carried out at the beginning of 2005. Among the 60 interviewed farmers, 38 (63%) use aquatic plants to fertilize their crops, mainly sweet potatoes, cassava, chili, tobacco, and vegetables. Rice and peanuts are not commonly fertilized by this way. This practice is particularly popular in the communes located in the North of the lagoon, where the proportion of lands fertilized in this way is sometimes higher than 20%, whereas in the sandy zone between the lagoon and the sea, it is generally around 10 to 20%. The most used species are Najas indica, Vallisneria spiralis, Potamogeton malaianus plus various algae species. Following the farmers' estimations, the quantities actually used vary from 0.45 to 10 tons of fresh matter per year and per farm, with an average of 3.5 tons. The farmers are not at all conscious of the possible ecological impact of collecting plants for agricultural uses, particularly on the sustainability of the lagoon resources. Many of them believe that the plant biomass reduction that they have observed in recent years in the lagoon is mainly due to the development of aquaculture.
