| Abstract: | Recent studies have highlighted the agronomic and environmental importance of phosphorus (P) movement through the soil profile. 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, we collected nitrogen (N) and P transport data in run‐off and seepage (lateral subsurface return flow) from 13 field‐ and farm‐scale watersheds on Vertisols in Central Texas for a 14‐year period. For 2004–2017, seepage accounted for ~20% of the total surface flow, and nutrient concentrations were generally similar in run‐off and seepage. As surface run‐off contributed ~80% of the flow, it follows that median annual N and P loads in run‐off were significantly greater than in seepage for every watershed. N loads in both run‐off and seepage flow from cultivated land were an order of magnitude greater than in native prairie and improved pasture, and the highest run‐off 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 run‐off or seepage. Land use and watershed scale produced significant differences in seepage volume but did not affect run‐off volumes or total surface flow/rainfall. Although 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. And in terms of P, this contradicts the traditionally held scientific viewpoint that P movement through the vadose zone is unimportant agronomically and environmentally. |
