Eutrophication resulting from phosphorus (P) accumulation in water systems has been a worldwide concern for three decades. Agricultural soils are known to be an important non-point source of P in waterways. The objectives of this research are to identify agricultural management practices that reduce the risk of P loss from soils, and to investigate the underlying mechanisms of P retention and loss from soils. In the short term (4 years), dissolved P loads were not affected by tillage and were similar in corn (in a continuous corn rotation) and soybean (in a soybean/corn rotation) production systems. Soils amended with composted cattle manure had a greater P load than chemically fertilized soils. On average, 30% of the total P leached was in organic P forms, indicating that organic P compounds could also be problematic to water systems. Although manure application improved soil aggregation and thus may increase P retention by avoiding soil erosion, P loss through subsurface flow by leaching may be substantial. A simple soil test, either Mehlich-3 P or P saturation ratio can predict the P leaching potential, but water ponding on the surface of agricultural land could significantly affect the accuracy of the prediction. / The P adsorption data was fit with the Langmuir 2-surface model, which predicted that up to 90% of the native adsorbed P was distributed on the high-energy surface. Native adsorbed P in manured soils was weakly retained, as the binding strength coefficient was 50 times less in manured than chemically fertilized soil. This findings was confirmed by measuring P desorption, which showed that P desorption rate was almost 3 times greater from manured soils than from chemically fertilized soils. Manuring alters soil particle surfaces by increasing negative charge. This is the direct reason for less P adsorption and greater P desorption by manured soils. / The Langmuir 2-surface model and the adapted non-ideal competitive adsorption (MICA) model were equally good at modeling P adsorption data. However, the NICA model is more robust and can predict phosphate adsorption with changing soil solution pH. The simultaneously modeling of P adsorption and hydroxyl adsorption with the NICA model makes it a promising tool for analyzing competitive adsorption among anions in soils.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.100631 |
| Date | January 2005 |
| Creators | Jiao, You, 1966- |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Natural Resource Sciences.) |
| Rights | © You Jiao, 2005 |
| Relation | alephsysno: 002492957, proquestno: AAINR25178, Theses scanned by UMI/ProQuest. |
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