The role of non‐crystalline Fe in the increase of SOC after long‐term organic manure application to the red soil of southern China

Abstract

Because of the important role of soil organic carbon (SOC) in nutrient cycling and global climate changes, there has been an interest in understanding how different fertilizer practices affect the SOC preservation and promotion. The results from this study showed that long-term application of manure (21 years) could increase significantly the content of SOC, total nitrogen (N) and soil pH in the red soil of southern China. The chemical structure of SOC was characterized by using solid-state cross-polarization magic angle spinning (CPMAS) 13 C nuclear magnetic resonance (NMR) spectroscopy, and the aromatic C, ratio of alkyl C : O-alkyl C, aromaticity and hydrophobicity of mineral fertilizers N, P and K plus organic manure (NPKM) and organic manure (M) treatments were less than those of mineral fertilizer nitrogen (N) and mineral fertilizers N, P and K (NPK) treatments. Both poorly crystalline (Fe o ) and organically complexed (Fe p ) iron contents were influenced significantly (P < 0.05) by different fertilizers, and it was observed that NPKM and M treatments increased the non-crystalline Fe (Fe o -Fe p ) content. There was a significant (P < 0.01) positive correlation between soil organic C and non-crystalline Fe in both the surface (0-20 cm) and subsurface (20-40 cm) soils. The results suggested that non-crystalline Fe played an important role in the increase of SOC by long-term application of organic manure (NPKM and M) in the red soil of southern China.

Carbon Sequestration Potential Promoted by Oxalate Extractable Iron Oxides through Organic Fertilization

“…The increase in total SOC content resulted from direct C input from the organic fertilizers and indirect C input from the increased net primary production as indicated by the increased grain yields through organic fertilization (Wen et al, 2014). This is consistent with the findings that organic fertilization could significantly promote soil C sequestration and thus contributed to long-term soil fertility improvement Zhang et al, 2013;Zhou et al, 2009). In the present study, the significant (P < 0.001) positive correlation between Feo and SOC indicated that Feo may play an essential role in the sequestration of C in this typical rice-wheat rotation paddy soil.…”

“…9a), indicating that Feo could moderate the decomposition of SOC. This is consistent with findings of Zhang et al (2013), who reported that highly reactive non-crystalline Fe nanoparticles played an important role in the accumulation of SOC with a low alkyl C/O-alkyl C ratio after the long-term application of organic manure in the red soil of southern China. Furthermore, the positive correlation between Feo and the intensity of O-alkyl C (R 2 = 0.493, P = 0.004) may favor the accumulation of labile organic compounds in paddy soils (Eusterhues et al, 2011;Lalonde et al, 2012;Schwertmann et al, 2005).…”

“…Organic fertilization slightly increased the alkyl C/O-alkyl C ratio compared with the chemical fertilization alone from 0 to 10 cm, indicating that the SOC in the soil amended with organic fertilizers underwent greater decomposition than that with chemical fertilizer alone. This may be ascribed to a positive priming effect caused by organic fertilization, which increased the microbial mineralization of SOC by improving the growth and activity of soil microorganisms (Zhao et al, 2016), resulting in the production of organic acids that may be partly responsible for the increased intensity of carboxyl C (Zhang et al, 2013). Moreover, the alkyl C/Oalkyl C ratio increased with increasing soil depth, indicating that SOC in the deeper soil layers may be more degraded than that in the upper soil layers (Rumpel and Kögel-Knabner, 2011).…”

“…Adhikari and Yang (2015) proposed that reactive iron oxides selectively stabilized aliphatic over aromatic organic compounds because the hematite-bound aliphatic C was more resistant to reductive dissolution than the aromatic C. Eusterhues et al (2011) and Lalonde et al (2012) noted that reactive iron oxides preferentially preserved O-alkyl C by forming organo-iron complexes through co-precipitation. Additionally, recent insight into the C sequestration mechanism after the long-term organic fertilization into soils has shown that the increase in SRO minerals is mainly responsible Wen et al, 2014;Zhang et al, 2013). However, knowledge regarding the effect of different fertilization treatments on the biogeochemical cycles of iron oxides and specific organic compounds in paddy soils, and their implications for SOC sequestration is scarce.…”

In situ visualisation and characterisation of the capacity of highly reactive minerals to preserve soil organic matter (SOM) in colloids at submicron scale

“…Previous studies have shown that organic fertilisation increased the concentration of highly reactive Al and Fe minerals, which are strongly linked to the SOM preservation capability (Kögel-Knabner et al, 2008;Solomon et al, 2012;Yu et al, 2012;Zhang et al, 2013b;Vogel et al, 2014b). In this study, the soil sample from the MNPK-treated plot was rich in SOC (13.50 g/kg) and SON (1.70 g/kg).…”