Incidental phosphorus losses – are they significant and can they be predicted?

Abstract

Fresh applications of phosphorus (P) may cause incidental' losses of dissolved and particulate P forms in land runoff when rainfall interacts directly with fertilizers and manures which are spread, or excreted, onto the soil surface. Research indicates that when incidental P losses (IPL) occur, they often make the dominant (50±98 %) contribution to measured P loads in surface and sub-surface runoff from field plots, with increased risk of eutrophication where P-enriched runoff is routed directly to the watercourse. Rates of P loss are temporally and spatially very variable (< 1 to 25 % of total P applied) depending on the amount of P applied; the P release properties of the materials applied (% P extractable in water), the timing of storm events after application and the amounts of runoff generated. Large P applications left on the surface of wet, frozen, compacted, and intensively underdrained soils in high rainfall areas are particularly vulnerable to IPL. Concentrations of P in runoff are often greatest during the first storm event following P application, but can remain high for several weeks, or even months after application. Catchment scale impacts are more difficult to quantify due to the effects of dilution with runoff from fields without IPL, and the contributions of P from other sources. Approaches to predicting IPL are discussed and need to be improved in order to assess the contribution of IPL to catchment P loads in river basin management planning. Strategies to control IPL should focus on adoption of more sensitive management practices in fields with a high risk of rapid runoff or preferential flow, and are likely to very effective.Ereignisbezogene Phosphorverluste ± Sind sie signifikant und können sie verhergesagt werden?Eine gerade erfolgte Ausbringung von Phosphor (P) kann Ursache für ereignisbezogene ªepisodischeº Austräge an gelöstem und partikulärem P mit dem Abfluss sein, wenn Niederschlag direkt auf mineralischen oder organischen Dünger an der Bodenoberfläche trifft. Untersuchungen zeigten, dass diese ereignisbezogenen P-Austräge bei Auftreten oft den Hauptbeitrag (50±98 %) zu gemessenen P-Frachten in oberflächlichem und unterirdischem Austrag aus Parzellen ausmachen. Sie bedeuten ein erhöhtes Eutrophierungsrisiko, wenn die P-angereicherten Austräge direkt in Gewässer gelangen. Die Raten der P-Austräge sind zeitlich und räumlich sehr variabel (< 1 bis 25 % des insgesamt zugeführten P) und hängen ab von der Höhe der P-Zufuhr, den P-Freisetzungseigenschaften des aufgebrachten Materials (% wasserextrahierbarer P), dem Zeitpunkt des Niederschlagsereignisses nach P-Applikation und der Abflussmenge. Groûe applizierte P-Mengen, die auf der Oberfläche nasser, gefrorener, verdichteter und intensiv drainierter Böden in niederschlagsreichen Regionen verbleiben, sind besonders von ereignisbezogenen P-Austrägen betroffen. Die Konzentrationen an P im Abfluss sind oft am grössten während des ersten Starkniederschlagsereignisses nach der P-Applikation; sie können jedoch über mehrere Wochen oder sogar Monate...

Phosphorus Desorption Dynamics in Soil and the Link to a Dynamic Concept of Bioavailability

“…Soil Science and Environmental Quality Team, Institute of Grassland and Environmental Research (IGER), Okehampton, Devon, EX20 2SB, UK 'Incidental' is a term used to describe phosphorus (P) mobilisation that occurs when rain and runoff interact directly with fresh applications of P to the soil surface, such as those from fertiliser, manure or excreta (Haygarth and Jarvis, 1999;Withers et al, 2003). 'Incidentals' involve pools of P that are conceptually distinct from those mobilised from the soil itself, although from the time of application, freshly applied P undergoes an equilibration with soil P pools; this means that there is a relatively small and diminishing time period for incidental mobilisation to occur.…”

Aspects of phosphorus transfer from soils in Europe

“…However, although no-till and plant cover can reduce sediment loss, P stratification in soil (surface enrichment) is significantly increased (Hussain et al, 1999;Zibilske et al, 2002;Saavedra et al, 2007), which may determine an increase in the ratio of potentially eutrophicant P (bioavailable) to total P in runoff (Pusstinen et al, 2005), since the soil surface has the greatest influence on runoff P concentration (Dougherty et al, 2004). Also, under no-till systems, incidental P losses, which is the mobilization which occurs when rain and runoff interact directly with fresh applied P to the soil surface (Haygarth and Jarvis, 1999;Withers et al, 2003), can be of particular significance. Stratification and incidental losses of P can be also important factors affecting P transfer in surface runoff from intensive pasture systems (Nash et al, 2000;Dougherty et al, 2004).…”

Phosphorus Fertilizer Rate, Soil P Availability, and Long-Term Growth Response in a Loblolly Pine Plantation on a Weathered Ultisol

“…The fertilizer may have been lost very early in the study due to "incidental" [48,49] or "event-specific" [50] losses, which are generally overlooked due to the relative importance of soil P status and long-term fertilization of agricultural and pastoral lands toward determining soil P loss [51]. One nearby (20 km) weather station in Oakdale, Louisiana, reported over 250 mm of precipitation in April 1982, including one storm of over 120 mm of rain [36].…”

“…Given that the fertilizer was applied in April 1982 and that the surface soil permeability is only 1.5 to 5 cm h −1 [25], a storm of this magnitude may have caused much of the P loss. When event-specific losses occur, they can account for 50%-98% of the total P lost in surface and subsurface runoff [49], and under high rates of superphosphate application, reduced contact of the fertilizer with the mineral soil creates a situation whereby high intensity rainfall can easily transport the fertilizer P [49,52]. Situations like this essentially render the high soil P sorption capacity ineffective.…”