Is there any way to identify which type of phosphorus (P) is exported from agricultural watersheds?

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I am developing a phosphorus (P) budget for an agricultural watershed (Haean waershed, 6175 ha, South Korea). Chemical fertilizers and organic matter (compost and manure) are the main sources of P in my study site. In addition, the soil of the watershed is characterized as sandy loam. P sorption capacity of manured sandy loam soils is lower than chemical fertilized soils. Additionally, the mean P concentration is 0.041 and 0.691 mg/l for dry and wet season (more than half of the annual precipitation is concentrated during summer monsoon season (July-August)) respectively.

Is there any way to identify which part of P - Org. P or Inorg. P is mainly exported from the watershed ?

Taxonomy

7 Answers

  4. Different types of phosphates can be identified using Raman Spectroscopy. Using standard P compounds you may be able to characterise in detail the different types of phosphorus present. You may need to work with a university to get access to this testing technique and discuss how organic P might be differentiated.

  6. Is there any way to identify which type of phosphorus (P) is exported from agricultural watersheds?

    Yes. Analyse the water leaving watershed for the component parts of total P. i.e. phosphate-P (often called dissolved reactive P [DRP] or soluble filterable P), dissolved organic P, particulate P and total P [TP].  Total P gives the maximum P in the sample, particulate P gives the solids component and DRP gives the inorganic component. The dissolved organic P component can be analysed as for total P after filtration and subtracting the DRP. These results will give you the form of the P leaving the watershed.

    Note that DRP is rapidly bound to iron particles in the soil / sediment or may be assimilated into aquatic plants including algae. Consequently, there may not be any (or perhaps 10) then filtering before analysing the DRP content using the TP method.

    You may be able to distinguish between chemical fertilisers and organic matter (compost and manure) by analysing the oxygen-18 isotope stable isotopic signature of the DRP once it is extracted.