Tu Pham Khanh

Fertilization Capacity of Aquatic Plants Used as Soil Amendments in the Coastal Sandy Area of Central Vietnam

In Central Vietnam, and more especially in Thua Thien Hue Province, aquatic plants are used empirically by some farmers as an external source of organic matter to improve fertility of sandy soils. The fertilization capacities of aquatic plant species [Najas indica (Willid.) Cham., Najas minor All., Vallisneria spiralis L. (Michx.) Torr., Hydrilla verticillata (L.f.) Royle, Potamogetum malaianus Miq., Myriophyllum spicatum L., Enteromorpha flexuosa (Wulfen) J. Agardh, Rhizoclonium kerneri Stockmayer, and Eichhornia crassipes (Mart) Solms] were assessed from a pot trial including soils amended with aquatic plants (5 g dry matter kg−1 soil) and soils supplied with increasing rates of urea nitrogen (N) fertilizers. Rice (Oryza sativa L.) at a vegetative stage was used as a convenient bio‐extractor. The fertilization capacity of aquatic plant amendments was calculated from aboveground biomass and from N accumulated in shoots as compared to treatments receiving only inorganic N fertilizers. Najas indica (Willid.) Cham. and Hydrilla verticillata (L.f.) Royle showed the greatest fertilization capacity, equivalent to 170–180 mg urea‐N kg−1 soil as estimated from biomass yield, whereas a lesser fertilization capacity, equivalent to less than 100 mg urea‐N kg−1 soil, was observed for Myriophyllum spicatum L., Enteromorpha flexuosa (Wulfen) J. Agardh, Rhizoclonium kerneri Stockmayer, and Eichhornia crassipes (Mart) Solms. This study provides quantitative data on the fertilization capacity of aquatic plants found in the coastal area of central Vietnam, which can improve this empirical practice and alleviate local agro‐environmental constraints related to the lack of organic matter in farming systems.