Transfer functions for phosphorus and potassium soil tests and implications for the QUEFTS model

Elise Van Eynde,Rob N.J Comans,Bas Kempen,Mirjam S Breure,Ellis Hoffland

doi:10.1016/j.geoderma.2021.115458

Elise Van Eynde, Rob N.J Comans + Show 3 more

Open Access

https://doi.org/10.1016/j.geoderma.2021.115458

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Abstract

Multi-element soil extractions such as Mehlich 3 (M3) have gained popularity in recent years, but comparing outcomes to other soil testing methods is not always straightforward. In this study, extraction mechanisms of M3, Olsen and neutral 1 M ammonium acetate (AA) soil tests were explored and transfer functions were derived between P-Olsen and P-M3 as well as between K-AA and K-M3. Soils from tropical and temperate areas were used to derive these P and K transfer functions and were evaluated separately. The application of these transfer functions for tropical soils was evaluated by using them as input for the Quantitative Evaluation of the Fertility of Tropical Soils (QUEFTS). AA and M3 generally extracted similar amounts of K, but relations between K-AA and K-M3 were different for tropical and temperate soils. For tropical soils, the transfer function did not require additional parameters besides K-M3 to predict K-AA, but for temperate soils inclusion of clay content and pH was needed. This difference between tropical and temperate soils was explained by clay mineralogy. The relation between P-Olsen and P-M3 in tropical soils was found to be dependent on pH, Al-M3, Fe-M3 and Ca-M3. P-Olsen and K-AA values, calculated with their respective transfer functions, were used as input for QUEFTS. The yields predicted with measured P-Olsen and Exch. K were used as benchmark. For 63 out of 81 soil samples, predicted maize yields with transfer functions deviated less than 10% from the benchmark. The largest deviations from the benchmark were found for low P-Olsen and K-AA values, which corresponds to QUEFTS maize yield predictions up to 3000 kg ha−1. We conclude that a M3 extraction results and soil pH can reliably be transferred to, and thus replace P-Olsen and K-AA determinations with the functions developed for tropical soils. The transfer functions can be used to generate input for the QUEFTS model with minor effects on yield predictions, thus expanding its applicability in cases where only M3 extraction results are available.

Highlights

Multi-element soil extractions have gained popularity in recent years
The relation between K extracted by M ammonium acetate (K-AA) and K-Mehlich 3 (M3) in tropical soils could be described with a single linear relationship
We conclude that a Mehlich 3 (M3) extraction can be used effectively to predict K extracted by 1 M ammonium acetate (K-AA) in tropical soils, using the K transfer function developed in this study

Summary

Introduction

Multi-element soil extractions have gained popularity in recent years. Their convenience and lower costs make them more attractive than the use of separate single element extractions (Iatrou et al, 2014). Single element extraction methods, such as Olsen, Bray, H2O and CaCl2, have been developed to quantify available soil P pools (Wuenscher et al, 2015), whereas plant available or exchangeable K and other cations have commonly been estimated using 1 M ammonium acetate (Barbagelata, 2006). Soil nutrient test results should relate to bioavailability, i.e. the amount of a nutrient available for plant uptake over a growing season They are used as input for decision support tools such as the Quantitative Eval uation of the Fertility of Tropical Soils (QUEFTS) model, which requires P-Olsen and K determined by a 1 M ammonium acetate extraction to estimate the soil’s capacity to supply a crop with P and K (Janssen et al, 1990). The focus in this study will be on comparing P and K in M3 to P-Olsen and K in ammonium acetate extractions, respectively

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