Location: Watershed Physical Processes ResearchTitle: The role of soil surface water regimes and raindrop impact on hillslope soil erosion and nutrient losses Author
Submitted to: Natural Hazards
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/18/2013
Publication Date: 3/14/2013
Citation: An, J., Zheng, F., Romkens, M.J., Li, G., Yang, Q., Wen, L., Wang, B. 2013. The role of soil surface water regimes and raindrop impact on hillslope soil erosion and nutrient losses. Natural Hazards. 67:411-430. DOI 10.1007/s11069-013-0570-9. Interpretive Summary: Soil and nutrient loss from agricultural land are most often considered from a scale in which soils, crops, topography, and rainfall are uniform. In reality, and depending on scale, conditions relative to these characteristics and situations vary substantially. On sloping land the surface water regime changes appreciably from top to bottom of fields with zones of standing and flowing water, positive (seepage) and negative (infiltration) surface soil water pressures. These different hydraulic surface conditions affect soil and nutrient movement differently. In this article, the results of a rainfall simulator study are discussed in which the effect of different commonly observed hydraulic surface conditions on soil and nutrient movement were simulated. These were: (1) a free-drainage soil profile with rainfall (FD+R), (2) a saturated soil water profile with rainfall (SA+R), (3) artesian seepage under a 20 cm soil water pressure without rainfall (SP), and (4) seepage under 20 cm water pressure with rainfall (SP+20). Also, two surface conditions were considered: (1) a sealed or crusted surface (exposed soil surface), and (2) a seal- or crust-free surface (protected surface). The results showed: (1) eroded soil was enriched in nutrients relative to that of the original soil; (2) nutrient concentrations and losses varied little with a change in the soil/water regime but tended to follow the sequence SP+R > SA+R > FD+R; (3) raindrop impact was more appreciable on nutrient loss with soil than with runoff; and (4) the effect of raindrop impact on the covered plot reduced soil loss by 57%-74%. This information will be helpful for better management practices involving deep tillage and no-till on the slopes of the Black Soil Region n China.
Technical Abstract: Soil surface water regimes on hill-slopes may appreciably affect soil erosion and nutrient losses. Different water regimes are often prevalent on different parts of the slope and therefore may affect these losses differently. A laboratory rainfall simulator study was conducted to determine the effect of the slope surface water regime on soil erosion, nitrogen (N), and phosphorus (P) losses by runoff on a silty clay loam soil of the Black Soil Region in Northeast China. Four soil surface water regimes were studied: a freely draining soil profile with rainfall (FD+R), a saturated soil water profile with rainfall (Sa+R), artesian induced seepage under 20 cm of soil water pressure without rain (SP20), and seepage under 20 cm of soil water pressure with rainfall. Also, two surface treatments were included–one with and the other without a nylon net surface cover to study the effect of rain drop impact. Nitrogen was applied at a rate of 200 kg/ha and phosphorus at a rate of 90kg/ha. Sixty mm of rainfall was applied at an intensity of 60 mm/h on a 5° slope. Results show that the surface water regime appreciable affected soil erosion and nutrient loss. Runoff from the SP20+R and Sa+R treatments were, respectively, 1.79-1.99 and 1.53-1.81 times greater than that from the FD+R treatment while soil losses were, respectively, 1.50-1.74 and 1.12-1.74 times greater. Nutrient concentrations and losses in runoff followed the sequence SP+R >Sa+R >FD+R. Seepage flow was relatively low and caused little soil loss, but contained appreciable amounts of nutrients. NOsub3-N, NHsub4-N, and POsub4-P concentrations in runoff from the SP20 treatment were respectively, 200x, 40x, and 7.3x that of the FD+R treatment. The eroded soil content in runoff from the FD+R, Sa+R, and SP+R treatments ranged from 48.6-76.5, 58.6-80.6, and 55.4-140.6 mg/l, respectively, for NOsub3-N, 13.8-18.2, and 14.5-48.4 mg/l for NHsub4-N, and 0.40-1.87, 1.81-3.03, and 2.30-2.47 mg/l for POsub4-P, respectively. Although the eroded soil was enriched in nutrients relative to that of the original soil, nutrient concentrations and losses varied little with a change in the soil water regime. Raindrop impact on the nylon net cover reduced soil loss by 57%-74%. Mineral N and P losses reduced about 15% and 21%. Effects of rain drop impact were more appreciable on nutrient loss with soil than in runoff. These findings are expected to lead to better soil management practices involving deep tillage and no-till on hill slopes of the Black Soil Region in Northeast China.