Soil organic matter and clay zeta potential influence aggregation of a clayey red soil (Ultisol) under long-term fertilization

Yangbo He,Rui Huang,Yao Wang,Mingxuan Yang,Waqar Ali

doi:10.1038/s41598-021-99769-w

Abstract

The effect of soil organic matter (SOM) on aggregation of variably-charged red soils (Ultisol) through clay zeta potential is not fully understood. Therefore, the objectives of this study were to investigate the SOM effect on the clay zeta potential and soil aggregation after fertilization. Soils under 17 years of fertilization (manure, NPK + straw, NPK, and control (CK) were adjusted by KCl solution to reach varying soil pH and concentration in order to determine clay zeta potential, cations, and aggregate size distribution. The SOM content and C-functional groups by 13C-NMR analysis were also determined. Results showed that the negative zeta potential displayed a bell-shaped pattern with increasing concentration of KCl, but displayed different amplitude of variation among treatments. Manure had the highest zeta potential value and its degree of variation in relative to the value at KCl concentration of 0.1 mol L−1 (19%), NPK + straw and NPK treatments were similar, and CK was the least. Greater negative zeta potential for manure treatment was attributed to higher SOM content, aromatic-C functional groups, and their greater concentrations of Ca2+ and Mg2+ than did the CK. As a result, higher SOM and clay zeta potential yielded in less release of amount of soil particles (< 10 μm) (r = − 0.46*) and enhanced water stable macroaggregates for manure instead of NPK + straw. Long-term manure fertilization would be suggested as a conservation practice for red soil due to its increase in soil aggregate stability and negative zeta potential in subtropical climate.

Highlights

Stable aggregates are important to improve soil permeability and restrict soil erosion
Compared to CK, soil organic matter (SOM) increased by 125%, 54.6% and 0.3% for manure, NPK + straw and NPK, respectively
Similar SOM distribution patterns occurred among dry-sieved aggregate sizes

Summary

Introduction

Stable aggregates are important to improve soil permeability and restrict soil erosion. Small particles of some types of Ferralsols with high SOC in subtropical climate of Brazil were difficult to re-flocculate when they were released from mechanical breakdown of m acroaggreates[12]. Ultiol or Oxisols in these studies possessed high amount of variably-charged soil oxides compared to soils in temperate regions having 2:1 type of clay minerals with permanent c harges[13], which might change the intensity of imbalance in charge on soil particles and the intenal forces between particles. It is necessary to understand the variably-charged soil minerals’ interaction with SOM and their subsequent effect on soil surface electrochemical properties such as zeta potential (a main factor influencing soil internal force). The electrostatic repulsive force between adjacent soil particles can be weakened less severely in the presence of a high content of SOM in subtropical soils than temperate soils[8]. A decrease in negative zeta potential was generally consistent with an increase in clay dispersion, confirming the important zeta potential effect on soil s tructure[9]

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Results

Conclusion