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Phosphorus losses in furrow irrigation runoff
D T Westermann1, D L Bjorneberg, J K Aase
1USDA-ARS, Northwest Irrigation and Soils Research Lab, Kimberly, ID 83341, USA. dtw@kimberly.ars.pn.usbr.gov
Journal of Environmental Quality
|June 13, 2001
Summary
Reducing soil erosion is key to minimizing phosphorus (P) runoff into waterways. Higher soil P levels directly correlate with increased dissolved reactive phosphorus (DRP) in surface irrigation runoff, emphasizing the need for erosion control measures.
Area of Science:
- Environmental Science
- Soil Science
- Water Quality
Background:
- Phosphorus (P) is a primary driver of eutrophication in freshwater ecosystems.
- Surface runoff from agricultural lands is a significant source of P entering streams, rivers, and lakes.
- Understanding the link between soil P availability and runoff P is crucial for managing water quality.
Purpose of the Study:
- To evaluate the relationships between soil P availability indices and various P fractions in surface irrigation runoff.
- To determine how manure, whey, or commercial fertilizer applications influence soil P levels and subsequent runoff P losses.
- To identify key factors controlling P transport in surface irrigation runoff.
Main Methods:
- Soil samples were analyzed for water-soluble P, Olsen P, and iron-oxide extractable P (FeO-Ps) under varying P management histories.
- Runoff samples were analyzed for dissolved reactive phosphorus (DRP), iron-oxide extractable P (FeO-Pw), total P, and sediment concentrations.
- Data from two irrigation seasons (1998 and 1999) were combined due to lack of significant differences.
Main Results:
- Flow-weighted average runoff DRP and FeO-Pw concentrations showed a linear increase with rising soil P test concentrations.
- Average runoff total P concentration was not directly correlated with soil P tests but was linearly related to sediment concentration.
- Stepwise regression identified sediment, soil lime, and soil organic P (Olsen method) as significant predictors of total runoff P.
Conclusions:
- Increased soil P availability directly elevates dissolved P fractions in irrigation runoff.
- Sediment transport is a critical pathway for total P loss in surface irrigation runoff.
- Implementing soil erosion control measures is essential for mitigating P pollution from irrigated agricultural lands.