Distribution of Nitrogen and Phosphorus in Arable and Forest Stand along the Boundary of Upstream Daechung Reservoir

This investigation was conducted to provide the control methods of N and P by observing the distribution of nitrogen and phosphorus in arable and forest stands along the boundary of upstream Daechung Reservoir in which water quality properties caused by N and P from land uses was not extensively studied.To do this, we selected three different soil zone such as arable (paddy and upland), orchard, and forest stands including pine and larch of which inputs of N and P have been known to be different due to their foliage properties.Soil samples were collected from surface and subsurface to measure soil physical and chemical properties.The results showed that the soil textures of investigation sites are loamy sand and sandy loam and the stone ratio of both forest stand are approximately 38.7%.The organic matter content in both forest stands was above 5.6% while that of the paddy and upland are less than 3%.Soil pHs are strongly acidic except for orchard of which it is above 5.7 but less than 6.64.However, pHs of all the sites slightly increased from May to October.The amount of NO3 -and NH4 + as water soluble phase is less than that of exchangeable phase in paddy while that of NO3 -and NH4 + as exchangeable phase is greater than that of water soluble phase in upland and the forest stands of pine and larch.For the proportions of phosphorus remained as water soluble-and exchangeable phase depending on the total P, the proportion of water soluble in paddy and pine stand was greater than 10% while those of exchangeable P are less than 10% in upland, orchard, and larch stands.From these results based on the amount and the proportion of N and P in soil, we could assume that N and P from the both pine and larch stands may contribute the deterioration of water quality of Daechung Reservoir.