Comparison of the Machigin and CAL Methods for Extraction of Plant Available P in Soils

ABSTRACT

Fertilizer recommendations for phosphorus (P) are generally based on the soil content of plant available P and the amount of P exported by the harvested crop. In countries of the former Soviet Union (SU), a widespread method is the Machigin extraction. The relationships between soil P contents extracted with this and other European methods are not well established. Here, we compare the Machigin soil P extraction method with the Calcium Ammonium Lactate P(CAL) procedure that is commonly used in Central Europe. Both methods were tested with 94 soil samples originating from Kyrgyzstan, Ukraine, and Germany. Overall, the P amount extracted with the CAL method was 2.8 times higher than that extracted with the Machigin method. However, using results from all analyzed individual soil samples, the relation between P(CAL) and P(Machigin) showed large scatter and an R² of only 0.364. Differing relations between P(CAL) and P(Machigin) were observed for soils with pH >7 and <7. However, these are overshadowed by differences between the three geographic groups of the soil samples. The estimated soil P fertility classes for the Machigin extraction were mostly higher than for the German (CAL) procedure, resulting in lower fertilizer recommendations for the Machigin method. To improve the accuracy of conversion between both methods, evaluation of laboratory proficiency tests (i.e. analysis of the same soil samples in different laboratories with the same methods) of the Machigin method should be useful.

KEYWORDS:

• Calibration
• inter-laboratory comparisons
• phosphate fertilizer
• phosphorus
• recommendation
• soil-P tests

Acknowledgements

We appreciate the input of Kristin Bothe (Rostock) and Dima Kostarev (Zakhidnyi Buh Private Company, Pavliv Village, Radekhiv District, Lviv Region, Ukraine) during the early stages of this work, and the support of DAAD, German Academic Exchange Service, Bonn, Germany.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The work was supported by the Deutscher Akademischer Austauschdienst (DAAD) - German Academic Exchange Service.