Altered humin compositions under organic and inorganic fertilization on an intensively cultivated sandy loam soil

Authors: XU, JISHENG - Chinese Academy Of Sciences; ZHAO, BINGZI - Chinese Academy Of Sciences; CHU, WENYING - Old Dominion University; MAO, JINGDONG - Old Dominion University; Olk, Daniel - Dan; XIN, XIULI - Chinese Academy Of Sciences; ZHANG, JIABAO - Chinese Academy Of Sciences

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/22/2017
Publication Date: 12/1/2017
Citation: Xu, J., Zhao, B., Chu, W., Mao, J., Olk, D.C., Xin, X., Zhang, J. 2017. Altered humin compositions under organic and inorganic fertilization on an intensively cultivated sandy loam soil. Science of the Total Environment. 601-602:356-364. doi: 10.1016/j.scitotenv.2017.05.205.

Interpretive Summary: Carbon contributes to several important properties of soil. Much of soil carbon is held strongly within the soil and therefore difficult to study, preventing adequate understanding of its behavior and cycling. We studied the most stable portion of carbon in an agricultural soil. Its composition was found to change with type of fertilizer applied to the soil, and it likely contained both plant and microbial materials. Its general properties appeared to show influences of the soil microbial populations. These results provide new information regarding the factors of carbon accumulation in soil. They will assist researchers who study the cycling of stable soil carbon and land managers who wish to promote carbon accumulation in the soil.

Technical Abstract: Humin is the largest and also the least understood fraction of soil organic matter. The humin structure and its correlation with microbiological properties are particularly uncertain. We applied advanced solid-state 13C nuclear magnetic resonance (NMR) spectroscopy to investigate the structural changes of humin in response to long-term balanced fertilization on a Calcaric Fluvisol in the North China plain. The relationships between humin structure and microbiological properties such as microbial biomass, microbial quotient (qmic) and metabolic quotient (qCO2) were also studied. Long-term fertilization promoted the aliphatic nature of humin, causing increases in O-alkyl, anomeric and NCH functional groups and decreases in aromatic C and aromatic C–O groups. All these changes were more prominent for treatments of organic fertilizer (OF) and combined mineral NPK fertilizer with OF (NPKOF) relative to the Control and NPK treatments. Fertilization also decreased the alkyl/O-alkyl ratio, aromaticity and hydrophobic characteristics of humins, suggesting a more decomposed and humified state of humin in the Control soil. Generally, the humins were predominately composed of alkyl (24–27% of all C), aromatic C (17–28%) and O-alkyl (13–20%) with a considerable (35–44%) proportion of aromatic C being nonprotonated and the vast majority of O-alkyl and anomeric C being protonated, indicating multiple sources of humin from plant and/or microbial tissues, black carbon as well as the organic fertilizer. Moreover, the soil microbiological properties had strong correlations with functional groups of humin. Particularly, microbial biomass C was a relatively sensitive indicator, having positive correlations with oxygen-containing functional groups, i.e., COO/N–C=O and protonated O-alkyl C, and negative correlations with nonprotonated aromatic C. The qmic and qCO2 were also significantly positively correlated with NCH and aromatic C–O, respectively. Our results suggest fertilization caused structural changes in humin, probably because of feedback mechanisms between microbiological properties and humification.