Submitted to: Journal of Environmental Quality
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/9/2006
Publication Date: 7/6/2006
Citation: Kleinman, P.J.A., Srinivasan, M.S., Dell, C.J., Schmidt, J.P., Sharpley, A.N., Bryant, R.B. 2006 Role of Rainfall Intensity and Hydrology in Nutrient Transport via Surface Runoff. Journal of Environmental Quality. 35:1248-1259 Interpretive Summary: The loss of nutrients from agricultural soils in runoff water is a major water quality concern that has prompted considerable research on how field management affects the nutrient content of runoff. Rain simulation studies have been widely used to evaluate management effects on nutrient runoff, as they enable the control of hydrologic variability which often confounds runoff studies. However, controlling such variability can also bias research results by favoring certain conditions. This study examined the effect of hydrologic and landscape factors on nutrient losses in runoff. By conducting rain simulation experiments under different hydrologic conditions and landscape positions, this study provides insight into the relevance of traditional rain simulation experiments in describing processes controlling nutrient transport. Findings indicate the limitation of extrapolating traditional rain research to predict the export of nutrients from agricultural soils. At the same time, the study clearly affirms the critical source area concept now dominating agricultural nutrient management: it is the coincidence of high nutrient availability and high transport potential that control nutrient loss from soil, not simply nutrient availability alone.
Technical Abstract: Loss of soil nutrients in runoff accelerates eutrophication of surface waters. This study evaluated phosphorus (P) and nitrogen (N) in surface runoff in relation to rainfall intensity and hydrology, modified by soil properties and landscape position. Experiments were initiated on 1 x 2 m plots at foot-slope (6%) and mid-slope (30%) positions within an alfalfa-orchard grass field in Pennsylvania’s Ridge and Valley Province. Rain simulations (2.9 and 7.0 cm hr-1) were conducted under wet, spring and dry, late-summer conditions. An elevated water table at the foot-slope during the spring resulted in less rain required to generate runoff and elevated runoff volumes, compared with runoff from the well-drained mid-slope in spring and at both landscape positions in late summer. Phosphorus in runoff was primarily in dissolved reactive form (DRP, averaged 71% of total P), with mean DRP concentrations related to soil test P and possibly plant sources. Nitrogen in runoff was primarily in the form of NO3 (averaging 77 % of total N). Hydrologic variables, not chemistry, were primarily responsible for trends in mass N and P losses. Larger runoff volumes from the foot-slope produced higher losses of total P (0.08 kg ha-1) and N (1.35 kg ha-1) than did runoff from the mid-slope (0.05 total P kg ha-1; 0.48 kg N ha-1), particularly under wet, spring-time conditions. Nutrient losses were significantly greater under the high intensity rainfall due to larger runoff volumes. Describing source factors alone is insufficient to explain differences in nutrient loss potential in complex landscapes.