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The equivalence of the Calcium‐Acetate‐Lactate and Double‐Lactate extraction methods to assess soil phosphorus fertility
Author(s) -
Laak Michael,
Klingenberg Uwe,
Peiter Edgar,
Reitz Thomas,
Zimmer Dana,
Buczko Uwe
Publication year - 2018
Publication title -
journal of plant nutrition and soil science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.644
H-Index - 87
eISSN - 1522-2624
pISSN - 1436-8730
DOI - 10.1002/jpln.201700366
Subject(s) - chemistry , linear regression , soil fertility , mathematics , fertilizer , extraction (chemistry) , comparability , phosphorus , soil water , soil test , statistics , chromatography , soil science , environmental science , organic chemistry , combinatorics
A large variety of extraction methods are used worldwide for the estimation of “plant‐available P” in soils. In Germany, the standard extractants are Calcium‐Acetate‐Lactate (CAL) and Double‐Lactate (DL). Until now there is no validated transformation procedure available and studies on the comparability of both methods have reported conflicting evidence. The uncertainty about the equivalence of CAL‐P and DL‐P hinders a direct comparison of the P fertility status and P fertilizer recommendations across Germany. Based on 136 datasets for soil samples from an interlaboratory comparison program and three P fertilization field trial sites, for which plant‐available P had been determined by both the CAL and DL method, we assessed the comparability of both extraction methods and derived simple and multiple regression equations to transform DL‐P into CAL‐P values. On average, DL extracted 30% more P than CAL. However, this strongly depended on soil pH and carbonate content. A simple linear regression model explained 70% of the variance. However, if simple linear regression models were fitted to pH‐specific samples (pH range 4.5 to 7.0) the R 2 increased to 0.96. Based on an independent validation dataset ( n = 48) we demonstrated that such pH‐specific models were more accurate than models that did not consider pH when transforming DL‐P to CAL‐P values. Multiple regression results showed that out of soil pH, C org , N t , and C : N ratio, only soil pH improved the model. The transformation equations in this study provide a step towards an improved comparability of P fertility status assessments of soils across Germany.