Examining correlations between organic carbon chemistry and δ15N abundance in soils across an aridity gradient

Dr Mark Farrell1, Ms Janine McGowan1, Mr Steve Szarvas1

1CSIRO, Glen Osmond, Australia

Storage of carbon and nitrogen (collectively soil organic matter; SOM) in soil is heavily influenced by climate change. Generally, more SOM is stored in soils due to greater inputs by plants in areas with higher rainfall. Organic nitrogen however, is mineralised by microbes into the more accessible nitrate which would show a tendency to leach out of soil in high rainfall. The effects of moisture changes on soil organic C and N across a 900 km aridity gradient in South Australia was examined. This transect was established under the Terrestrial Ecosystem Research Network (TERN) and our aim was to understand the transformations of soil organic C and N within it. Samples were collected from 42 long-term monitoring sites following the mainland portion of the Adelaide geosyncline, from the Fleurieu Peninsula in the south to Murnpeowie Station in the north. The sampling was carried out in the 2016 Austral autumn, comprising a composite of 20 individual surface soil samples from within a 25×25 m plot established at the corner of each site. Soil organic matter chemistry was quantified by 13C-CP/MAS NMR and δ15N was measured by EA-IRMS. The alkyl/o-alkyl (A/OA) ratio derived from NMR measurements is a measure of how much SOM is turned over or decomposed. The A/OA ratio was weakly positively correlated with aridity (R2 = 0.148), whereas δ15N showed a much stronger relationship (R2 = 0.515). Taken together, these data indicate greater cycling of SOM and fewer fresh inputs as aridity increases.


Janine McGowan is a Research Officer at CSIRO in Adelaide and has 30 years’ experience in soil organic matter characterisation through analytical expertise in soil fractionation, carbon and nitrogen analysis and NMR spectroscopy.

Janine has a Bachelor of Science degree (Hons) in Organic Chemistry from The University of Adelaide.

Steve Szarvas is a Research Support Officer at CSIRO and has over 20 years of experience in various analytical methods involving nitrogen and carbon, particularly related to soil and organic matter (SOM) turnover and more recently, food provenance. His expertise includes the use of N-15 tracers and subsequent isotopic analysis using Isotope-ratio mass spectrometry techniques. Steve has an Associate Diploma in Analytical Chemistry from the University of South Australia.

Soil organic matter distribution in a floodplain forest

Dr Mark Thomas1, Dr Helen Glanville2, Ms Linda Broekman3, Dr Mark Farrell1

1CSIRO, Glen Osmond, Australia, 2Keele University, Keele, UK, 3Forestry Corporation of NSW, Deniliquin, Australia

Soil organic matter is recognised as being central for healthy soil and broader ecosystem functionality, yet its variability and factors that dive this at the landscape scale are less well understood. This is particularly the case in floodplain forest systems where there is significant local and landscape-scale variation in relation to vegetation type and inundation patters and history, along with underlying geomorphology. Here we report the findings of research carried out in Koondrook-Perricoota State Forest in the NSW Riverina, situated between Barham in the north-west and Moama in the south-east, bordering the River Murray. The forest is very low-lying, with a height gradient of approximately 10 m across its whole length, and thus floodwaters are generally slow-moving following mostly subtle local-scale topographic gradients. We established a series of 10 toposequences throughout the forest capturing local scale variation, and collected soils from the 0-30 cm layer in order to understand how inundation history and seasonality affect multiple soil health indicators, including SOM. Preliminary analyses reveal a 3-4 fold difference in soil organic carbon (SOC) concentration between the highest (3.04%) and lowest (0.89%) concentrations, and a 2-3 fold difference (0.06 – 0.17%) in total nitrogen concentrations, resulting in an average C:N ratio of 11.1 across the 40 sites. These results along with data from ongoing analyses will be discussed.


Dr Mark Thomas has >25 years of experience in land resource assessment in Australia and overseas. From a strong foundation in soil science and modern land evaluation Mark innovates to deliver and translates this knowledge to management challenges, principally in the areas of sustainable agriculture and natural resources. As a result of this knowledge transfer there is reduced uncertainty in land-based decision making and increased confidence in public investment and regulation. This has been delivered into some of the most pressing contemporary land issues of the day: northern Australia for new resource regulation and agricultural investment; national bedrock depth mapping to underpin economic objectives and environmental modelling; the gas extraction industries to assess the impacts of extraction activities on communities and primary industries; new sustainable land planning support tools for developing countries, and; new data and methods for wise dryland farming decisions.

Dr Mark Farrell is a Principal Research Scientist and leads the Soil Biogeochemistry Team at CSIRO, based in Adelaide. He has worked in a range of agricultural and natural systems, ranging from the Australian outback to the Arctic and Antarctic. His interests lie in soil organic matter, the microbial community that it harbours, and the ecological functions it delivers, particularly nitrogen supply. Prior to joining CSIRO 9 ½ years ago, he worked at Lancaster and Bangor universities in the UK, where he also attained his PhD.

Comparison of constituents of dissolved organic matter in soil and lake water by two-dimensional HPLC

Dr Masakazu Aoyama1

1Hirosaki University, Hirosaki, Japan

Dissolved organic matter (DOM) is a major form of organic matter in the hydrosphere and plays an important role in the transport of trace metals such as iron. A significant portion of the hydrosphere DOM is considered to be leached from the soil. The purpose of this study was to clarify what kind of DOM constituent is leached from soil to hydrosphere by comparing the constituents of soil and lake water DOM samples. Lake DOM samples were prepared from the upstream and downstream lakes of the Iwaki River in the northern part of the Honshu island, Japan, and soil DOM samples were from representative soils of the river basin. For HPLC analysis, the hydrophobic fractions of DOM prepared by adsorption of acidified samples onto DAX‐8 resin were used. For comparison, DAX-8 adsorbed fulvic acids were obtained by alkali extraction from the same soils. The constituents of DAX-8 adsorbed DOM fractions and fulvic acids were analyzed by two-dimensional HPLC using hydrophilic interaction chromatography (HILIC) followed by reverse phase chromatography (RP-HPLC). For the DAX-8 adsorbed fractions of soil and lake water DOM, the proportion of the constituents eluting in the most hydrophobic region upon HILIC was smaller than for soil fulvic acids. Upon RP-HPLC, sharp peaks exhibiting only UV absorption and broad peaks exhibiting featureless spectra with the absorbance decreasing gradually from the UV region to the visible region were eluted for the soil DOM and fulvic acids. In contrast, the lake water DOM mainly had broad peaks, and the number of sharp peaks was smaller than the soil DOM and fulvic acids. It was concluded that the main constituents of the DOM that leached from soil to the hydrosphere were dark-colored organic substances having absorption in the UV and visible regions and were more hydrophobic than soil fulvic acids.


Dr. Masakazu Aoyama is a Professor of Soil Science at the Fuculty of Agriculture and Life Science, Hirosaki University. His current research interest is the molecular compositions of DOM and humic substances in soil and aquatic environments. He has been developing chromatographic methods for the analysis of DOM and humic substances.

‘Hidden’ soil carbon at risk of erosion in the rangelands

Dr Susan Orgill1,2,3, Dr Cathleen Waters1, Dr  Craig Strong2

1NSW Department Of Primary Industries, Wagga Wagga, Australia, 2Fenner School, Australian National University , Acton, Australia, 3Graham Centre for Agricultural Innovation, Wagga Wagga, Australia

Wind erosion preferentially removes fine organic carbon (OC) and nutrient rich soil. Enriched dust can be transported long distances resulting in a net loss from the terrestrial ecosystem and reduced soil fertility, moisture holding capacity and soil aggregate stability which may feedback to promote more erosion. Changes in the structure and spatial distribution of vegetation associated with land management can accelerate soil erosion and carbon loss. This study was located in the semi-arid rangelands of western New South Wales (NSW) where over 2.7M ha of land has been contracted to sequester carbon (C) in woody vegetation under the Emission Reduction Fund. We investigated the location and form of OC within the soil matrix and assessed the capacity of soil to protect OC from erosion under different vegetation communities. Surface soil samples were collected from plots comprised of five replicates of three densities (high, medium and low) for Pine (Calitris glaucaphylla), Box (Eucalyptus populnea) and Mulga (Acacia aneura) communities. Soil samples (0-1 and 1-5cm) were dry and wet sieved, then each aggregate class was analysed for total OC (dry combustion) and OC fractions (MIR). Vegetation community significantly influenced aggregate stability, size distribution, SOC concentration and fractions, with Box communities having a higher degree of aggregation and SOC compared with Pine and Mulga. Box communities are located along drainage lines and these areas typically have higher soil moisture and nutrient content and typically accumulate water-transported sediment high in OC. The high concentration of SOC (specifically humic-OC) within the high proportion of <0.83mm (dry sieved) aggregates, and poor aggregate stability in the surface 1cm of all soils highlights the vulnerability of SOC to loss via erosion. Thus our results suggest it is important to account for potential loss of SOC (via wind erosion) when considering the quantum abatement in western NSW.

Biography: Dr Susan Orgill has worked in the field of soil management for NSW Department of Primary Industries (DPI) since 2005. Susan is based at the Wagga Wagga Agricultural Institute and leads the Soils South team. She is passionate about delivering industry and farm-ready research, and her research relates to strategies to increase organic carbon accumulation and storage, and nutrient cycling in agricultural soil.

Climate, soil organic carbon and soil erosion – quantifying change in a large catchment

A/Prof. Greg Hancock1, Dr Veikko Kunkel1, Dr Tony Wells1, Dr  Cristina Martinez2

1The University Of Newcastle, Callaghan, Australia, 2School of Agriculture and Food Sciences, The University of Queensland, , Australia

There is much to learn regarding its spatial and temporal distribution as well as how soil organic carbon moves through the landscape. Of particular interest is how soil organic carbon movement is related to soil erosion and deposition. This study examines the spatial distribution of soil organic carbon in a (562 km2) catchment in relation to soil erosion and deposition from 2006 to 2019. The results demonstrate that the spatial distribution of soil organic carbon concentration on average is stable. However, differences were found in soil organic carbon when concentrations were compared between samples collected at different time periods. The environmental tracer caesium-137 (137Cs) was used to assess erosion and deposition patterns. We found a significant relationship between soil organic carbon change and erosion and deposition at each sample point. That is, sample sites with an increase in soil organic carbon corresponded with an increase in 137Cs concentration (depositional sites) while locations with a decrease in soil organic carbon corresponded with a decrease in 137Cs concentration (erosional sites). The results were confirmed using a Monte-Carlo assessment. The reason for the soil organic carbon change and soil movement was the largest rainfall event (since 1969) in the area. The findings suggest that soil organic carbon can be translocated by significant rainfall events.


Organic materials flow and nutrient balance analyses at different landscapes of a watershed in Tigray, Northern Ethiopian highlands

Dr Gebreyohannes Girmay1, Mr Tesfay Berihu1, Mr Henok Shiferaw1, Mr Mulugeta Sebhatleab1

1Mekelle University, Mekelle, Ethiopia

Soil fertility depletion is the major cause for declining per capita food production in Ethiopia. We evaluated a material and associated nutrient flows at different landscapes (lower, middle and upper) and household wealth groups (poor, medium and rich) at Maileba watershed in Tigray, northern Ethiopia. Comparison of the domestic organic material inputs and processed outputs indicated an annual total organic material balance of about -12.09 t/ha for upper, -8.04 t/ha for middle, and -5.41 t/ha for lower landscapes. The associated annual total organic C, N and K depletion for the rich household groups was about 598kg C/ha, 38 kg N/ha and 16kg K/ha in the upper, 621kg C/ha, 42kg N/ha and 22kg K/ha in the middle and 603kg C/ha, 44kg N/ha and 14kg K/ha/yr in the lower landscapes. The poor household group extract about 438kg C/ha, 36kg N/ha and 11kg K/ha in the upper; 293kg C/ha/yr, 22kg N/ha and 9kg K/ha in the middle, and 368kg C/ha/yr, 30kg N/ha and 12kg K/ha in the lower landscapes. Product harvest, crop residue removal and run-off associated material outflows were the major causes for nutrient depletion in the watershed. The organic material and soil nutrient stocks of the various landscapes are rapidly declining particularly in the upper landscape position of catchments. The rich (better of) households are the potential target groups to contribute more to conservation of watersheds than the poor. A properly planned nutritional management and integrated upland organic farming should receive due attention on the mountainous areas of Ethiopia and east Africa.

Biography: Gebreyohannes Girmay has his expertise in soil fertility management systems focusing on exploring techniques for improving soil quality and health. He teaches and advices post graduate students in the soil science, dryland ecology and resource management, dryland agronomy, sustainable watershed management, and dryland agroforestry and land restoration programmes in Mekelle University, Ethiopia. His current research activities focus on integrated soil fertility management, carbon sequestration in soils, reservoir conservation and sediment use, and land evaluation for irrigation.

Loss of organic carbon in erosion and as dissolved organic carbon from agricultural soil

Ms Noora Manninen1, Ms Sanna Kanerva1, Ms Riitta Lemola2, Ms Eila Turtola2, Ms Helena Soinne3

1University Of Helsinki, Helsinki, Finland, 2Natural Research Institute Finland, Jokioinen, Finland, 3Natural Research Institute Finland, Helsinki, Finland

The loss of organic carbon (OC) weakens soil structure and increases the risk of erosion, thus decreasing soil productivity and the quality of surrounding waters. Water can transport OC from agricultural soils as dissolved organic carbon (DOC) or as attached to erosion material. A global decline in agricultural soil OC content has been suggested to result from intensive land management within the past decades. In addition to enhanced soil organic matter mineralization, tillage increases the risk of erosion by weakening soil structural stability, and thus, is likely to increase the loss of soil OC. However, agricultural managements that increase topsoil OC content may increase the annual DOC loads. The aims of this research were to quantify discharge-transported OC loads from agricultural land in Boreal zone, and to study the effects of soil managements on OC loss. We collected discharge samples from surface runoff and subsurface drainage for two years (2015-2017) on two clay soil sites in Finland. The studied agricultural managements were plough, no-tillage, mineral and manure fertilization, and permanent grassland. Annual discharge-exported total OC loads from cultivated plots were 20–70 kg ha-1 and from permanent grassland 50–80 kg ha-1. The share of DOC load was dominant (67–96% for cultivated plots and 90% for grassland plots) compared to erosion-transported OC load. Annual precipitation varied substantially between the years, thus effecting the loads. Total OC loads were higher from ploughed soil compared to no-tillage management only on the first year. Further, the OC loads did not differ between mineral and manure fertilization. The total OC loads in subsurface drainage were higher than in surface runoff when soil was ploughed. Topsoil (0-5 cm) OC% correlated negatively with erosion-transported OC load and positively with DOC load, when cumulative discharge volume was considered typical.

Biography: In my PhD thesis I´m studying the loss of organic carbon (OC) in discharge water from agricultural Boreal soils. We study the chemical characteristics of soil OC under different agricultural managements, the OC loads transported by discharge water, and the impacts of OC loss on soil productivity and water quality.

Lateral transport of SOM through landscapes

Prof. Asmeret Asefaw Berhe1

1University Of California, Merced, Merced, United States

Most of the earth’s terrestrial ecosystem is composed of sloping landscapes, where soil organic matter dynamics is partly controlled by the mass movement events that laterally distribute topsoil. Accurate estimation of the global soil carbon stock or the potential of soils to sequester atmospheric carbon dioxide are complicated by the effects of soil redistribution on both net primary productivity and decomposition. In this presentation, I will discuss: (1) why and how soil erosion can constitute a C sink; and how soil erosion is being considered within the context of global climate models; (2) the role of soil erosion on determining spatial distribution and stocks of SOM, stability, and stabilization  mechanisms; (3) emerging understanding of the role of soil erosion in soil nitrogen dynamics; and I will conclude the presentation by highlighting remaining knowledge gaps in our understanding of the  role of soil erosion in  soil phosphorus dynamics, and SOM dynamics in temperate and arctic ecosystems.

Biography: Dr. Asmeret Asefaw Berhe is a Professor of Soil Biogeochemistry at the Department of Life and Environmental Sciences, University of California, Merced. Prof.

Berhe received her Ph.D. in Biogeochemistry from the University of California (UC), Berkeley; M. Sc. in Resource Development (Political Ecology) from Michigan State University, and B. Sc. in Soil and Water Conservation from University of Asmara, Eritrea.

Dr. Berhe was a University of California President’s Postdoctoral Fellow at UC Berkeley and UC Davis, and a NASA Earth System Science Graduate fellow at UC Berkeley.

Prof. Berhe’s research focuses on biogeochemical cycling of essential elements (esp. carbon, nitrogen, and phosphorus) and furthering our understanding of how the soil system regulates atmospheric climate.

Prof. Berhe is a recipient of several awards and honors including the National Science Foundation’s CAREER award, the Young Investigator Award from Sigma Xi, the Hellman Family Foundations award for early career faculty, and is a member of the inaugural class of the US National Academies of Science, Engineering and Medicine’s New Voices in Science, Engineering, and Medicine. Prof. Berhe is the Chair of the US National Committee on Soil Science at the National Academies; serves in the Leadership board of the Earth Science Women’s Network; and currently is an Associate Editor for the Journal of Geophysical Research – Biogeosciences

Transport of soil-derived dissolved organic matter (DOM) via surface runoff and fracture flow in a cropland loamy soil during natural rainfalls

Dr Chen Liu1, Dr. Qing-song Xian1, Prof. Xiang-yu Tang1

1Institute of Mountain Hazards and Environment, Chinese Academy of Sciences, Chengdu, China

Being crucial for predicting the impact of C inputs on a watershed in rainfall events, an understanding of the dynamics and characteristics of soil carbon export, mainly in the form of dissolved organic matter (DOM), from the soil under particular land use types, particularly those associated with underground flows is still largely lacking. A field study was carried out using a 1500 m2 slope farmland plot in the hilly area of Sichuan Basin, Southwest China. The discharge of surface runoff and fracture flow was recorded and samples were collected in four representative rainfall events. For DOM characterization, concentration of dissolved organic carbon (DOC) and absorbance/excitation-emission matrix (EEM) fluorescence were analyzed. Soil water potential was also determined using tensiometers for understanding the runoff generation mechanisms. The DOCs for both surface and fracture flow showed significant responses to rainfall, with hydrological path being the primary factor in determining DOM dynamics. EEM-PARAFAC analyses indicated that the soil DOM mainly consisted of two terrestrial humic-like components with peaks located at Ex/Em 270(380)/480 nm (C1) and 250(320)/410 nm (C2), respectively. Concentrations of these components also responded strongly to rainfall, fluctuating in good agreement with the corresponding DOCs. Although there was no change in the presence of the components themselves, their relative distributions varied during precipitation, with the C1/C2 ratio increasing with the proportion of soil pre-event water. As the dynamic changes of soil-derived DOM characteristics can be successfully captured using spectroscopic techniques, they may serve as a tracer for understanding the hydrological paths for soil carbon transport in a specific soil during rains.

Biography: Dr. Chen Liu is a scholar working at the Key Laboratory of Mountain Surface Processes and Ecological Regulation, Institute of Mountain Hazards and Environment, CAS, China. She has made research contributions in understanding the environmental behavior of the microcontaminants, their interactions with the soil and the transport hydrology with a goal to decrease the microcontaminants’ environmental risk. She got her M.S. and Ph.D. degrees both in environmental engineering from Sichuan University and has worked at the CAS institute since 2012.

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