Document Type : Complete scientific research article
Authors
1
Soil Science Department, Faculty of Agriculture, University of Zanjan, Zanjan, Iran.
2
Professor, Dept. of Soil Science, University of Zanjan
3
Department of Soil Science, Razi University, Kermanshah, Iran.
Abstract
Background and Objectives: Soil clays are recognized as essential soil minerals for organic matter stabilization. Clays have a significant influence on soil organic matter dynamics. Clays, forming clay-organic matter stable complexes and deactivating extracellular enzymes, protect organic matter against microbial degradation in soils with high clay content. As an abiotic factor, the amount of clays affects the microbial decomposition rate of organic materials and the size of soil organic matter pools. The effects of soil texture on soil organic matter dynamics have been investigated in many studies. Still, research showing the effects of clay type is rare, and the impacts of exchangeable cations in these regards are unknown. This research was conducted to understand better the effect of the type and amount of soil clays and the type of exchangeable cation on organic carbon retention.
Materials and Methods: Materials and Methods: Consequently, this work experiment was carried out to understand better the clay type, content, and exchangeable cations on soil organic carbon retention. Different clays (vermiculite and zeolite) were saturated with Na, Ca, and Al cations to prepare homoionic Na-, Ca-, and Al-clays of different clay mineralogy. Then, the homoionic clays of different clay mineralogy were mixed with pure sand in different ratios to obtain artificial soils with varying types of clay and contents and exchangeable cations. Alfalfa plant residues were incorporated into the artificial soils, and the soils were inoculated with microbes from natural soil and incubated in the dark at a temperature of 25 °C for six months. The factorial experiments, each with three replications and completely randomized designs (CRD), were used to assess the effects of clay type and content and exchangeable cations on organic carbon dynamics. The experiment consisted of two types of clays (vermiculite and zeolite), four clay contents (zero, 15, 30, and 45%), and three exchangeable cations (Na, Ca, and Al).
Results: This study showed the significant effects (p < 0.01) of clay type and content and exchangeable cations on the mineralization of organic carbon, microbial biomass, and concentrations of carbohydrates in the soil. Organic carbon mineralization was higher in pure sand than in soils containing 15%, 30%, and 45% clays. Organic carbon mineralization was higher in soils with vermiculite than in soils with zeolite. The highest percentages of mineralized carbon and microbial biomass carbon were measured in soils with Ca, and soils with Al had the highest concentrations of carbohydrates.
Conclusion: The results of this study indicate that organic matter and microbial biomass are stabilized in soils through interaction with clays, and a small amount of clays slows organic matter decomposition significantly and reduces carbon dioxide emission from soils. Exchangeable cations influence microbial biomass and carbon dynamics by controlling the microbial population's size and activity by modifying microbial habitats' physicochemical characteristics.
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