Speciation and sorption of phosphorus in agricultural soil profiles of redoximorphic character

Karen Baumann,Sabry M Shaheen,Mohsen Morshedizad,Elena Heilmann,Yongfeng Hu,Jianxu Wang,Jörg Rinklebe,Shan-Li Wang,Peter Leinweber,Peter Gros

doi:10.1007/s10653-020-00561-y

Abstract

Controlled drainage is considered as a soil management tool to improve water supply to crops and reduce nutrient losses from fields; however, its closure may affect phosphorus (P) mobilization in soil. To assess the P mobilization potential, three soil profiles with redoximorphic features were selected along a slight hill in Northern Germany. Soil samples from three depths of each profile were characterized for basic properties, total element content, oxalate- and dithionite-extractable pedogenic Al, Fe and Mn (hydr)oxides, P pools (sequential extraction), P species [P K-edge X-ray absorption near-edge structure (XANES) spectroscopy] and P sorption behavior. In topsoil (~ 10 cm depth), labile P (H2O-P + resin-P + NaHCO3-P) accounted for 26–32% of total P (Pt). Phosphorus K-edge XANES revealed that up to 49% of Pt was bound to Al and/or Fe (hydr)oxides, but sequential fractionation indicated that > 30% of this P was occluded within sesquioxide aggregates. A low binding capacity for P was demonstrated by P sorption capacity and low Kf coefficients (20–33 {text{mg}}^{{1 - n_{text{f}} }} ,{text{L}}^{{n_{text{f}} }} ,{text{kg}}^{ - 1}) of the Freundlich equation. In the subsoil layers (~ 30 and ~ 65 cm depth), higher proportions of Al- and Fe-bound P along with other characteristics suggested that all profiles might be prone to P mobilization/leaching risk under reducing conditions even if the degree of P saturation (DPS) of a profile under oxic conditions was < 25%. The results suggest that a closure of the controlled drainage may pose a risk of increased P mobilization, but this needs to be compared with the risk of uncontrolled drainage and P losses to avoid P leaching into the aquatic ecosystem.

Highlights

In Germany, draining wet and waterlogged land for the establishment of agriculturally used fields is a common practice
The results suggest that a closure of the controlled drainage may pose a risk of increased P mobilization, but this needs to be compared with the risk of uncontrolled drainage and P losses to avoid P leaching into the aquatic ecosystem
The sequence of the soil horizons differed for the three profiles and was typical for a stagnic cambisol (Braunerde-Haftpseudogley) at the upper-slope position, a haplic stagnosol (Normpseudogley) at midslope position and a colluvic stagnosol (PseudogleyKolluvisol) at the toe-slope position according to the

Summary

Introduction

In Germany, draining wet and waterlogged land for the establishment of agriculturally used fields is a common practice. In northern Germany, climate change results in the decrease of precipitation during growing season and extreme precipitation events (Madsen et al 2014; Svoboda et al 2015). To mitigate these extremes, controlled drainage is considered as an opportunity to retain moisture in fields for improving crop performance (Tolomino and Borin 2019) and to control diffuse phosphorus (P) losses from fields at watershed scale (Carstensen et al 2019; Dagnew et al 2019). Other studies detected decreased P loads in controlled drainage water (Wesstrom and Messing 2007; Jouni et al 2018)

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Conclusion