Phosphorus buffering capacity of substrate clays and its significance for plant cultivation

Abstract

Peat is commonly used as the main component of horticultural substrates, but it has a very low buffering capacity for the anionic macronutrient phosphorus (P), which can be increased by the addition of clays. The aim of this study was to characterize the P adsorption capacity of different substrate clays and to evaluate its significance for plant P uptake. Substrate clays were characterized with a single-point batch experiment and adsorption and desorption isotherms. The data were fitted to the Langmuir equation for a calculation of the maximum adsorption capacity. Additionally, the contents of oxalate extractable Fe and Al (SFe ox + Al ox ) were determined. The influence of a varying P adsorption capacity of the clays on the P availability to plants in the respective peat-clay substrates and pure peat was investigated in a growth experiment with Impatiens walleriana fertigated with 0, 17, and 35 mg P L -1 solution, respectively. The observed and calculated (Langmuir) P adsorption capacity of the clays could be well-characterized by both the batch experiment and the adsorption isotherms and was highly correlated with the SFe ox +Al ox . A higher P adsorption capacity of the clay amendment in mixed substrates resulted in a lower P concentration in the substrate solution, while the CAT extractable P concentration (P CAT ) was the same. Plant growth and shoot P concentrations were enhanced in the substrates, showing a higher P adsorption capacity, since plants were able to take up the whole amount of P CAT , and also part of the non-CAT extractable P. However, the release rate was too low to ensure optimal plant growth, which was in accordance with the result of the desorption experiment. The absolute extent of P release was increased with the increasing P adsorption capacity of the clays and higher degree of P saturation (DPS).

Soil phosphorus dynamics along a loess–limestone transect in Mihla, Thuringia (Germany)

“…Furthermore, replacement of P anions by OH − and is probable in these substrata ( Binner et al, ; Prietzel et al, ). The deeper solifluction layers and the weathering layers are neutral to slightly alkaline, and high in carbonate (Tab.…”

“…The high EC also implies the presence of many ions in the soil solution. Thus, because of pH and carbonate OH − and might cause intensive P mobilization ( Binner et al, ; Prietzel et al, ) and, thus, high amounts of P dHCl .…”

“…This lateral variation in the P contents is unlikely to be explained by P inputs via fertilization. The high content of P dHCl throughout profile 11 might instead be due to the replacement of P anions by OH − ( Amberger , ; Binner et al, ). This could only affect the whole profile when the material is deeply moistened.…”

“…This applies for all the agricultural sites and could be explained by fertilization and biogenic P mobilization in the rhizosphere ( Barber , ; Kruse et al, ). Furthermore, organic residues and the applied liquid biogas manure can chelate Fe, Al, and Ca ions on the surfaces of oxides, thus preventing chemisorption of P in less easily soluble forms ( Oburger et al, ; Binner et al, ; Kruse et al, ). Still, we also found high P cHCl and P AR contents in the plough layers, what might partly be due to organic residues from harvest.…”

Could oxalate‐extractable phosphorus replace phosphorus fractionation schemes in soil phosphorus prospections?—A case study in the prehistoric Milseburg hillfort (Germany)

“…Schwertmann (1964) proposed an extraction with ammoniumoxalate to determine easily soluble pedogenetic iron (Fe) oxides within soil samples. This method may also be used for the determination of P (Binner, Dultz, & Schenk, 2015;Prietzel, Klysubun, & Werner, 2016) because pedogenetic oxides of Fe and aluminum (Al) are regarded as the major P sorption agents within soils (Barber, 1995;Weihrauch & Opp, 2018). Thus, oxalate-extractable P (P-ox) would indicate the amount of P stored within a soil by sorption processes (Eichler-Löbermann, Köhne, & Köppen, 2007;Leinweber, Meissner, Eckhardt, & Seeger, 1999).…”