Application of the nitrogen outflow model for agricultural watershed: Studies on nitrogen outflow analysis in agricultural watersheds (2)
1998
Tabuchi, T. | Kuroda, H. | Shimura, M. | Kuroda, S.
Nitrogen concentration of stream waters are investigated in 13 small watersheds. Table 1 shows the land use and pig density of each wathersheds. NO3-N concentrations are quite different in watersheds, maximum value is 19.7 mg/l, and minimum value is 0.7 mg/l. It depends on land use and especially on pig density (Fig.3). NO3-N concentrations measured in ricegrowing season are lower than the values measured in non-ricegrowing season. During firegrowing season the water flowed out of upland area is almost irrigated and flooded within paddy fields in lowland area. Then nitrate caused from chemical fertilizer and pig slurry in upland is removed by both denitrification and aqua-plant uptake in the paddy. The nitrogen outflow model with nitrogen removal function of paddy fields were proposed in previous paper. Measured values are compared with the values calculated by this model. For non-ricegrowing season (Fig.5), and for ricegrowing season (Fig.7), the calculated values are nearly equal to measured values. Large difference is appeared in watershed L, where lots of pigs were fed in the past. It means that large amount of nitrogen flowed out of the pig farms in the past remains in the subsoil and groundwater
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