Relationship between nitrogen and phosphate surplus from agricultural production and river water quality in two types of production structure(Environment)

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We examined the relationship between nitrogen (N) and phosphate (P_2O_5) 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 P_2O_5 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 P_2O_5 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 P_2O_5 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 P_2O_5 to river water were higher in Omoigawa than Nakagawa. By excluding domestic sewage N and P_2O_5 in river water, we calculated the loads of non-point source N and P_2O_5. Non-point source N and P_2O_5 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).
社団法人日本土壌肥料学会の論文