Molecular speciation and transformation of soil legacy phosphorus with and without long-term phosphorus fertilization: Insights from bulk and microprobe spectroscopy

Abstract

Soil legacy phosphorus (P) represents a substantial secondary P resource to postpone the global P crisis. To fully utilize this P reserve, the transformation of legacy P speciation in a black soil with and without P fertilization for 27 years was investigated by chemical fractionation, molecular-level bulk (P K-edge X-ray absorption near-edge, XANES; solution 31P nuclear magnetic resonance) and microprobe (µ-X-ray fluorescence and µ-XANES) spectroscopy. Results from both fractionation and P bulk-XANES concordantly indicated that Ca2-P [Ca(H2PO4)2] acts as a reserve of labile P in response to soils with or without P fertilization. Cropping for 27 years depleted hydroxyapatite while enriched iron-bound P in soils irrespective of P application. Similar accumulation of soil organic P (Po), probably due to root residue inputs, occurred in both soils with and without P fertilization; the accumulated Po was present as orthophosphate diesters in soils with P fertilization more than in soils without P fertilization, suggesting that the release of labile Po was triggered by soil P deficits. These results provide vital information for agronomically and environmentally sustainable P management by demonstrating the potential crop availability of legacy soil P, which could reduce future P fertilization.

Soil Microbial Composition and phoD Gene Abundance Are Sensitive to Phosphorus Level in a Long-Term Wheat-Maize Crop System

“…However, the amount of organic P with the increased P addition is uncertain. The results showed that they can increase (Liu et al, 2017), decrease (Cade-Menun et al, 2017), or do not change (van der Bom et al, 2019) when P fertilization rates increased. In addition, most of the research has focused mainly on the relationship between available P in soil and phoD gene copy numbers, whereas the relationship between organic P and phoD abundance has not been very clear.…”

How Does Phosphorus Restriction Impact Soil Health Parameters in Midwestern Corn–Soybean Systems?

“…1). Liu et al (2017) showed an increase in organic P in the form of phosphomonoesters after 27 yr of no P fertilization, relative to both baseline and P fertilized samples. They attributed these increases to maize root-derived organic P. The hypothesis of increased root growth is also supported by several lines of evidence from physical indicators of soil health.…”

Options for Improved Phosphorus Cycling and Use in Agriculture at the Field and Regional Scales

“…Recent studies have shown that diesters may make up significantly more soil Po than has been previously assumed (Vincent et al, 2013; Smernik et al, 2015; Schneider et al, 2016; Zhang et al, 2017). Greater diester concentrations have been correlated with uncultivated or perennial systems (Hawkes et al, 1984; Condron et al, 1990; Mahieu et al, 2000) and leguminous crops (Guggenberger et al, 1996; Canellas et al, 2004; Schneider et al, 2016), while the effect of P fertilization is unclear as varied results have been observed (McDowell et al, 2007; Schneider et al, 2016; Liu et al, 2017; Abdi et al, 2019). This illustrates that further research is required to understand how crop rotation and agroecosystem management may affect soil Po forms, so that through management we may be able to promote Po forms that are readily mineralizable and potentially increase P availability in low‐input systems at appropriate times.…”