Abstract
Humic substances originating from various organic matters can ameliorate soil properties, stimulate plant growth, and improve nutrient uptake. Due to the low calorific heating value, leonardite is rather unsuitable as fuel. However, it may serve as a potential source of humic substances. This study was aimed at characterizing the leonardite-based soil amendments and examining the effect of their application on the soil microbial community, as well as on potato growth and tuber yield. A high yield (71.1%) of humic acid (LHA) from leonardite has been demonstrated. Parental leonardite (PL) and LHA were applied to soil prior to potato cultivation. The 16S rRNA sequencing of soil samples revealed distinct relationships between microbial community composition and the application of leonardite-based soil amendments. Potato tubers were planted in pots in greenhouse conditions. The tubers were harvested at the mature stage for the determination of growth and yield parameters. The results demonstrated that the LHA treatments had a significant effect on increasing potato growth (54.9%) and tuber yield (66.4%) when compared to the control. The findings highlight the importance of amending leonardite-based humic products for maintaining the biogeochemical stability of soils, for keeping their healthy microbial community structure, and for increasing the agronomic productivity of potato plants.
Highlights
IntroductionLeonardite is a product of atmospheric oxidation (part of the weathering process) of lignite (brown coal)
Leonardite is a product of atmospheric oxidation of lignite
According to our metagenomic analysis, the soil samples amended with coal-based humic acids displayed high microbial diversity and richness compared to the control
Summary
Leonardite is a product of atmospheric oxidation (part of the weathering process) of lignite (brown coal). This conversion occurs on a large scale, significantly impacting lignite properties in a negative manner, i.e., leading to structural weakness, excessive fragility, and loss of other inherent qualities of parental coal. The oxygen exposure of lignite leads to various heterogeneous oxidation reactions, mainly by impacting the aliphatic moieties, rather than the aromatic ones [3]. The details of the oxidation mechanisms of lignite are unclear, it is possible to propose that the introduction of additional carboxyl, hydroxyl, amino, and nitro groups plays a crucial role [4]. As a result of weathering, the valuable properties of the parental coal as a fuel source deteriorate
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