title: Effects of near-surface hydraulic gradients on nitrate and phosphorus losses in surface runoff.
abstract: Phosphorous (P) and nitrogen (N) in runoff from agricultural fields are key components of nonpoint-source pollution and can accelerate eutrophication of surface waters. A laboratory study was designed to evaluate effects of near-surface hydraulic gradients on P and N losses in surface runoff from soil pans at 5% slope under simulated rainfall. Experimental treatments included three rates of fertilizer input (control [no fertilizer input], low [40 kg P ha(-1), 100 kg N ha(-1)], and high [80 kg P ha(-1), 200 kg N ha(-1)]) and four near-surface hydraulic gradients (free drainage [FD], saturation [Sa], artesian seepage without rain [Sp], and artesian seepage with rain [Sp + R]). Simulated rainfall of 50 mm h(-1) was applied for 90 min. The results showed that near-surface hydraulic gradients have dramatic effects on NO(3)-N and PO(4)-P losses and runoff water quality. Under the low fertilizer treatment, the average concentrations in surface runoff from FD, Sa, Sp, and Sp + R were 0.08, 2.20, 529.5, and 71.8 mg L(-1) for NO(3)-N and 0.11, 0.54, 0.91, and 0.72 mg L(-1) for PO(4)-P, respectively. Similar trends were observed for the concentrations of NO(3)-N and PO(4)-P under the high fertilizer treatment. The total NO(3)-N loss under the FD treatment was only 0.01% of the applied nitrogen, while under the Sp and Sp + R treatments, the total NO(3)-N loss was 11 to 16% of the applied nitrogen. These results show that artesian seepage could make a significant contribution to water quality problems.
authors.affiliation: State Key Laboratory of Soil Erosion and Dryland Farming on Loess Plateau, Institute of Soil and Water Conservation, CAS and MWR, Northwestern Sci-Tech University of Agriculture and Forestry, Yangling, Shaanxi, 712100 China. flzh@ms.iswc.ac.cn
authors.forename: Fen-Li
authors.initials: FL
authors.lastname: Zheng
authors.forename: Chi-Hua
authors.initials: CH
authors.lastname: Huang
authors.forename: L Darrell
authors.initials: LD
authors.lastname: Norton
mesh_terms: D000383:Agriculture; D005308:Fertilizers; D009566:Nitrates / Q000032:analysis*; D010758:Phosphorus / Q000032:analysis*; D016062:Porosity; D011891:Rain; D012987:Soil; D012989:Soil Pollutants / Q000032:analysis*; D014872:Water Movements; D014873:Water Pollutants / Q000032:analysis*; D014881:Water Supply
chemical_list: D005308:Fertilizers; D009566:Nitrates; D012987:Soil; D012989:Soil Pollutants; D014873:Water Pollutants; D010758:Phosphorus