Nitrogen Leaching in Intensive Cropping Systems in Tam Duong District, Red River Delta of Vietnam

The environmental and economic consequences of nitrogen (N) lost in rice-based systems in Vietnam is important but has not been extensively studied. The objective of this study was to quantify the amount of N lost in major cropping systems in the Red River Delta. An experiment was conducted in the Red River Delta of Vietnam, on five different crops including rose, daisy, cabbage, chili, and a rice–rice–maize rotation during 2004 and 2005. Core soil samples were taken periodically in 20-cm increments to a depth of 1 m and analyzed for nitrate–nitrogen and ammonium–nitrogen. The results indicate appreciable leaching losses on N in high-rainfall and irrigation conditions, especially when fertilizer application was not well synchronized with crop N demand. Highest annual leaching losses of N were recorded in flowers with 185–190 mm of percolation and 173–193 kg N ha-1, followed by vegetable (cabbage and chili) with 120–122 mm of percolation and 112–115 kg N ha-1, while it was lowest in rice with about 50 kg N ha-1. We developed a simple N transport model that combined water and N movement through the soil profile. In most cases, the model accurately predicted the seasonal dynamics of N as well as N flow between soil layers and the amounts of N lost from the soil profile. The simulated results of N leaching with soil “puddling” conditions illustrate the advantage of an impermeable or hardpan layer in increasing water and nutrient use efficiencies in these soils. These model results also showed that it is possible to accurately estimate N losses with only a few parameters and helped us identify the risks of N leaching

New Approaches to Support Development of Sustainable Land Use Systems

In this paper, the land use planning cycle is introduced and some recent efforts at developing appropriate methodologies for supporting some of its distinct phases are illustrated. The examples still largely bear an academic character, but since there is increasing demand by policy makers for integrated land use analysis studies, they may serve as building blocks for development of operational methodologies for land use policy ormulation and analysis. Their potential impacts on planning procedures and chievement of land use objectives are high, particularly when they are further developed and operationalized in settings that allow participation and involvement of the various user group