Analysis of volatile organic compounds useful for soil evaluation in soybean fields — Significant changes during the blooming period

A research group comprising Professor Miyako Kusano of the School of Life and Environmental Sciences at the University of Tsukuba and RIKEN, Fukushima University, Hokkaido University, the University of Tokyo, Kyoto University, and other institutions has announced their research findings showing that the composition of soil volatile organic compounds (VOCs) (soil VOC profile) is useful for soil assessment in soybean fields. They collected soil samples over 3 years from soybean fields in Fukushima Prefecture under different soil conditions and analyzed VOC profiles thereof. Changes such as increased soil VOC levels in soybean plots were noted during the flowering period and correlated with other soil-related data. The findings are expected to contribute to sustainable agriculture. The study was published in the international journal Scientific Reports on September 4.

Sustainable agriculture requires appropriate soil improvement and use based on an understanding of soil health. A wide variety of organic compounds are present in the soil. VOCs, which are low-molecular-weight organic compounds that evaporate easily at normal temperature and pressure, are produced by various organisms and play an important role in physiological activity and interaction with the environment. Meanwhile, soil VOCs have not been adequately characterized in a comprehensive manner.

In this study, changes in soil VOC profiles from the pre-sowing period to the harvesting period were analyzed under different conditions (soil with no fertilizer, chemical fertilization, cow manure fertilization and no soybean cultivation) over 3 years in a soybean field at the Fukushima Agricultural Technology Center. VOC profiling was performed using headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry (HS-SPME-GC-MS). In addition, various data on soil physical properties, compounds and microorganisms were obtained.

As a result, approximately 200 VOC peaks were detected during the 3-year period, of which 36−62 candidate indicator compounds were found. Throughout the 3 years, the following five compound groups accounted for more than 80% of the total: alcohol, aldehyde, alkane, aromatic, and terpene classes. Unique VOCs were detected each year, revealing yearly diversity in soil VOC profiles. Cumulative levels of VOC profiles during the flowering period under cow manure conditions were twice as high as the normal levels.

Meanwhile, the relative VOC content was very low in the plots with no soybean cultivation. The research group also succeeded in identifying statistically discriminative soil VOCs, such as pentanoic acid. Furthermore, correlation analysis was performed between soil VOC profiles and six comprehensive soil-related datasets on element concentrations, microorganisms, metabolites and other factors (soil ionome, soil microbiome, root microbiome, soil metabolome, rhizosphere chemicals and soil physics).

The results showed that principal component 1 of the soil VOC profiles was significantly correlated with principal component 1 of each soil-related omics dataset. However, principal component 1 of the soil VOC profiles showed no correlations with principal component 1 of the rhizosphere chemicals and the root microbiome dataset.

The effects of soybeans on soil VOC levels during the flowering period may provide particularly useful information for assessing soil biological activity.

Kusano said, "In this study, soil samples were collected every 1−2 weeks for about 6 months from the sowing period to the harvest period, but I did not predict that this work would be so troublesome. I am so grateful to everyone who was involved in sampling. I also worked intensively with the data and struggled with processing the integrated omics data to find meaningful results. I am very pleased that we could demonstrate the potential of volatile compound profiling, also known as volatilomics, as a soil evaluation indicator."

Journal Information
Publication: Scientific Reports
Title: Soil volatilomics uncovers tight linkage between soybean presence and soil omics profiles in agricultural fields
DOI: 10.1038/s41598-024-70873-x