Comparison of nutrient loss pathways: Run-off and seepage flow in vertisols

Authors: Harmel, Daren; Smith, Douglas; Haney, Richard; ALLEN, P - Baylor University

Submitted to: Hydrological Processes
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/16/2019
Publication Date: 6/1/2019
Citation: Harmel, R.D., Smith, D.R., Haney, R.L., Allen, P.M. 2019. Comparison of nutrient loss pathways: Run-off and seepage flow in vertisols. Hydrological Processes. 2019:1-10. https://doi.org/10.1002/hyp.13474.
DOI: https://doi.org/10.1002/hyp.13474

Interpretive Summary: Recent studies are highlighting the agronomic and environmental importance of phosphorus (P) movement through the soil profile challenging the traditionally held scientific viewpoint. Thus, faced with challenges such as high-profile cases of P enrichment of surface water, better understanding of nutrient movement through soil is needed to better manage agricultural fertilizers and manures and their contribution to water quality degradation. In particular, field-scale research is especially needed in soils with preferential flow transport pathways. Thus, the present study conducted on a Central Texas research farm dominated by heavy clay soils collected data on nitrogen (N) and P transport in runoff and seepage flow from 13 field- and farm-scale watersheds for a 14 yr period. For 2004-17, seepage accounted for ~20% of the total surface flow, and nutrient concentrations were generally similar in runoff and seepage. Since surface runoff contributed ~80% of the flow, it follows that median annual N and P loads in runoff were significantly greater than in seepage for every watershed. N loads in both runoff and seepage flow from cultivated land were an order of magnitude greater than in native prairie and improved pasture, and the highest runoff and seepage P loads both occurred on cultivated land with organic fertilizer sources. Increasing watershed scale (size) did not to produce consistent patterns in N or P loss in runoff or seepage. Land use and watershed scale produced significant differences in seepage volume but did not affect runoff volumes or total surface flow/rainfall. While less significant in terms of total offsite flux, nutrient movement in vadose zones has important agronomic and environmental implications as considerable N and P are transported through and within the root zone and eventually offsite, which contradicts traditionally held views of flux and plant availability.

Technical Abstract: Recent studies are highlighting the agronomic and environmental importance of phosphorus (P) movement through the soil profile challenging the traditionally held scientific viewpoint. Thus, faced with challenges such as high-profile cases of P enrichment of surface water, better understanding of nutrient movement through soil is needed to better manage agricultural fertilizers and manures and their contribution to water quality degradation. In particular, field-scale research is especially needed in soils with preferential flow transport pathways. Thus, the present study conducted on a Central Texas Vertisol collected data on nitrogen (N) and P transport in runoff and seepage (lateral subsurface return flow) from 13 field- and farm-scale watersheds for a 14 yr period. For 2004-17, seepage accounted for ~20% of the total surface flow, and nutrient concentrations were generally similar in runoff and seepage. Since surface runoff contributed ~80% of the flow, it follows that median annual N and P loads in runoff were significantly greater than in seepage for every watershed. N loads in both runoff and seepage flow from cultivated land were an order of magnitude greater than in native prairie and improved pasture, and the highest runoff and seepage P loads both occurred on cultivated land with organic fertilizer sources. Increasing watershed scale (size) did not to produce consistent patterns in N or P loss in runoff or seepage. Land use and watershed scale produced significant differences in seepage volume but did not affect runoff volumes or total surface flow/rainfall. While less significant in terms of total offsite flux, nutrient movement in vadose zones has important agronomic and environmental implications as considerable N and P are transported through and within the root zone and eventually offsite, which contradicts traditionally held views of flux and plant availability.