|Huang, Chi Hua|
Submitted to: American Society of Agricultural Engineers
Publication Type: Proceedings
Publication Acceptance Date: 1/3/2001
Publication Date: 1/3/2001
Citation: Zheng, F., Huang, C., Norton, L.D. 2001. How near-surface moisture gradients affect phosphorous and nitrate losses. In: Eds. J.C. Ascough II and D.C. Flanagan. Soil Erosion for the 21st Century Proceedings. American Society of Agricultural Engineers. 3-5 January 2001, Honolulu, HI. p. 649-652. Interpretive Summary:
Technical Abstract: Phosphorous (P) and nitrogen (N) in runoff from agricultural fields are key components of non-point source pollution. Extensive efforts have been made to determine conditions that contribute to P/N losses. However, one factor, which may contribute significant P/N movement on the landscape but has not yet been quantified, is artesian seepage. A laboratory study was designed to evaluate artesian seepage effects on P and N losses from soil boxes. Experimental variables included three rates of fertilizer input: control, low (P: 40, N: 100 kg/ha) and high (P: 80, N: 200 kg/ha), and three near-surface hydrologic conditions: free drainage (Fd), saturation (Sa), and artesian seepage (Sp). Simulated rainfall of 50 mm/h was applied for 90 min and runoff samples were collected for dissolved P and nitrate-N analyses. The results showed that near-surface moisture gradients have great effects on nitrate-N and P losses. Comparing to drainage condition (Fd), nitrate-N concentrations in surface runoff from saturation (Sa), seep flow alone (Sp), and seepage with rain (Sp+R) ranged 41 to 62, 2242 to 9054, and 263 to 1110 times greater for control experiment, low and high fertilizer application rates, respectively. Similarly, average P concentrations from Sa, Sp, and Sp+R averaged 4 to 5, 8 to 16, and 7 to 8 times greater for low and high fertilizer inputs, respectively, as compared to Fd. These results showed that seepage condition may have a significant contribution to the water quality problem and efforts need to be focused on understanding and controlling hillslope seepage.