Relationship between nitrogen and phosphate surplus from agricultural production and river water quality in two types of production structure
2007
Mishima, S.(National Inst. for Agro-Environmental Sciences, Tsukuba, Ibaraki (Japan)) | Taniguchi, S. | Kohyama, K. | Komada, M.
We examined the relationship between nitrogen (N) and phosphate (P2O5) surplus derived from agriculture and river water quality. We selected two river basins; one was a paddy farming area (Omoigawa) and the other was an intensive livestock husbandry area (Nakagawa). Nitrogen and P2O5 surpluses, defined as the difference between their input and output on regional farmland, from farmland in Omoigawa were twice those of Nakagawa; the surpluses came mainly from chemical fertilizer use. Although N and P2O5 surpluses in Nakagawa were lower, Nakagawa had a large amount of non-utilized livestock excreta, twice the N surplus on farmland in Nakagawa. Residual N and P2O5 in the river basin, caused by surplus and non-utilized livestock excreta, were approximately 20% and 40%, respectively, higher in Nakagawa than in Omoigawa. Outflows of N and P2O5 to river water were higher in Omoigawa than Nakagawa. By excluding domestic sewage N and P2O5 in river water, we calculated the loads of non-point source N and P2O5. Non-point source N and P2O5 were higher in Omoigawa than Nakagawa. This inverse result might be caused by the different source of residual N (i.e. chemical N fertilizer or livestock excreta).
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