Hello
I am researching the mineral phosphorus fractions in calcareous soils. It is said that in the measurement of phosphorus by the Jiang and Gu method in calcareous soils, citrate prevents the formation of blue color in the solution, in the phosphorus trapped "OC-P" measurement stage.
-What is the reason for this problem? Is there a solution for that?
-What is the role of citrate in this reaction? Is it possible to replace it with another combination?
-Is there another method apart from Jiang and Gu method for measurement the same fractions in calcareous soil?
In calcareous soils , calcium phosphate is the most predominant fraction and holds the major reason for phosphorous unavailability. Application citrate soluble phosphorous fraction in calcareous soils indicates the intensity factor of phosphorous in such soils....
The amount of different P forms i.e. dicalcium -1 3 phosphates (Ca -P), octacalcium phosphates (Ca -P), Al-phosphates (Al-P), Fe-phosphates (Fe-P), occluded-P 2 8 (O-P) and P as apatite (Ca -P) found to be ranged from; 1.6-42.3, 72-314, 14.5-54.8, 8.4-34.8, 10 5.9-33.4 and 262-697 mg kg respectively. Phosphorus fractionated in following form
1. NaCl + NaOH-P,
2. citrate bicarbonate (CB-P),
3. citrate bicarbonate dithionate (CBD-P),
4. acetic acid-sodium acetate (OAc) and HCl (HCl–P)
The attribution of extracted P to specific solid phases is at best an approximation. For calcareous soils I suggest you look at papers by Andersson et al.
There is a color formation problem in citrate-bicarbonate-dithionite fraction. Youcan overcome this problem by adding extra ammonium molibdate solution. Have a look the article "Veli Uygur, Burak Durgun & Hüseyin Senol (2017): Chemical Fractions of Phosphorus: The Effect of Soil Orders, Soil Properties, and Land Use, Communications in Soil Science and Plant Analysis, DOI: 10.1080/00103624.2017.1341919. We said about this problem that "Citrate-bicarbonate-dithionite extraction method described by Kuo (1996) was employed to the residues from the previous extraction to solubilize P bound to free iron
oxides. Prior to the addition of colour reagent, 1.5 mL 5% ammonium molibdate solution was pipetted to air oxidized aliquots for 25 mL volumetric flasks (Weaver 1974) to improve color development.
I hope this will help you to solve your problem.
May consider the Hedley et al. P fractionation method for comparison. Article A Literature Review and Evaluation of the Hedley Fractionati...
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