Carbon and nitrogen analysis training

Abstract:

Nitrogen is one of the key nutrients in agriculture and its availability in soils drives crop production, specifically in the humid tropics. Judicious management of nitrogen inputs be they organic or inorganic requires knowing where the nitrogen in the soil is and how it flows through the plant-soil system, to increase resource efficiency and reduce environmental damage. Improvements in nitrogen management can substantially increase crop production specifically in low input systems relying on biological nitrogen fixation and low-cost external inputs derived from the circular economy, materials such as compost.

Further the Department of Agricultural and Biosystem Engineering at UGM has an active soil working group there, has just recently joined the GLOSOLAN activities and are eager to elaborate more on methods, skills and interlink laboratories across the country.

Our previous research has demonstrated the importance of these inputs in the Indonesian context in particular in the highly degraded post mining sites on Bangka island. So we aimed to transfer techniques and tacit knowledge embedded within to our counterparts in Indonesia. However possibly more importantly we want to work with them to further iterate the methodologies to suit their laboratory contexts and soil types. In this co-creation process we together develop quality assurance protocols and ensure that data is suitable for international publication.

Demonstration and hands-on training by Dr. Hood and Dr. Keiblinger on the soil feel test, to get an idea about soil texture as an additional site characteristic. For comparison not only sandy Bangka soils were used, but also more clayey soils from Kalimantan to “feel” the difference in between gritty and smooth samples and the ability to form a ball, ribbon, ring.

© Orracha Sae-Tun

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Implementation Period:

17.07.2023 – 06.08.2023

Project:

In 2018 a C/N analyser was donated from BOKU to UGM, and training with scientists, staff and students was conducted, for soil organic carbon analyses. The fact that just recently the Faculty of Agricultural and Biosystem Engineering at UGM has joined the GLOSOLAN (Global network of soil analyses, https://www.fao.org/global-soil-partnership/glosolan/en/), their soil working group was eager to elaborate more on methods, skills and interlink laboratories across the country.

To replace the use of wet-chemical analyses for organic Carbon via Wakley Black (cite), and total nitrogen via Kjehldal method (cite), the use of dry combustion elementary analyser allows a larger sample throughput, and is the method of choice also recommended by FAO (cite). However, a proper training to get high quality data is of crucial importance.

In order to further iterate the methodologies to suit their laboratory contexts and soil types, the implementation of conducting both organic Carbon and total Nitrogen analyses was a main focus during our stay and training.

The process included a full maintenance of the device, with a replacement of all PVC connection tubes that were already highly brittle and partly leaking to ensure the leak test of device is negative. Further the connected laptop and A/D converter were optimized for smooth samples runs (Figure 1, left).

The training started with some basic theory on soil sampling, and preparation including, the homogenization of samples via sieving and milling, as well as quartering to reduce sample amount and ensuring representative samples for further analyses (Figure 1, right). This was complemented with a demonstration of the quartering method by Dr. Rebecca Hood to reduce sample amount and ensure homogeneity as well as hands-on experience of soil sample preparation for analyses by the workshop participants using Bankga soil samples (Figure 2).

In the class, the lecturers and participants also discussed a set of additional on-site characteristics that should be elaborated beside soil/plant C and N measurements, to calculate SOC stocks ensure that data are suitable for international publication. Again, this was followed by demonstration and hands-on training of the soil feel test, to get an idea about soil texture (Figure 3). For comparison not only sandy Bangka soils were used, but also more clayey soils from Kalimantan to “feel” the difference in between gritty and smooth samples and the ability to form a ball, ribbon, ring (Figure 3, Figure 4). Also, the identification of the soil color using the Munsell color chart was part of the practical workshop to use the texture and color indicators for rough soil organic matter estimation (Figure 4).

To determine soil organic matter with the elementary analyser, the potential for inorganic carbon needs to be determined. This was discussed in the class that there is low potential in tropic soils due to full weathering of carbonates, but that agricultural management with lime or dolomite as well as ocean sediments are a source of carbonates that need to be considered for the analyses.

During the training course, the soil and crop (peanut) samples that were taken in February from the Bangka field experiment were used to do hands on activities in the laboratory and to process samples that are of scientific relevance that in the past were analysed in BOKUs laboratories.

As one of the treatments in the Bangka field experiment is the addition of dolomite, these samples were used for demonstration purpose, where soil samples were subject to HCl fumigation to get rid of carbonates (Figure 3). To do this, the soils are weighted into silver cups instead of tin cups and moistened with 10 µl of distilled water in HCl saturated desiccator for several hours. The samples can then be dried and covered in tin cups prior to measurements with the elementary analyser

To ensure accurate measurement, accuracy of the weight that is used for determining the sample amount that is combusted is critical. Hence a high precision microscale balance was donated to UGM, and the participants were trained in its maintenance (Figure 5). The proper use of the balance and the filling of tin cups with sample and reference material was part of the training procedure (Figure 6). The appropriate preparation of the tin-cups and sample weights for the measurements of total carbon and nitrogen was discussed for different sample material (soils, plants, food material). And the criteria for standards (non-hydrophobic chemicals), and references material (certified, soil and plant material) that is in a comparable range as the samples was elaborated. The calibration of the device, and the use of reference materials to calculate response factors, for quantification, was part of the introductory lecture, and repeated by hands on calculation of the results after the measurements, to apply it in practice.

A further critical issue is the local gas supply. In the past, the impurity of the oxygen gas supply did not allow for total N analyses using this elementary analyser. Still the purity of the oxygen gas has implications for the measurement of N in the samples. So the team had to figure out the background peak that comes from the gas, to be aware of the limit for detecting N in samples. This needed further changes in the measurement configuration. Beside the adjustment of oven temperature for peak separation quality, the time for loop flushing was reduced. To ensure the device can determine nitrogen even in low concentrations as found in soils. As nitrogen is one of the key nutrients in agriculture and its availability in soils drives crop production, specifically in the humid tropics. Improvements in nitrogen management can substantially increase crop production specifically in low input systems relying on biological nitrogen fixation and low-cost external inputs derived from the circular economy, materials such as compost. Our previous research has demonstrated the importance of these inputs in the Indonesian context in particular in the highly degraded post-tin mining sites on Bangka island, and has highlighted that methods currently used in Indonesia are in need some updating.

For the valve assembly pressurized air cannot be used due to the moisture background and potential corrosion of the valves, hence, N-gas was used. The connection of the gas bottle and the pressure unit, are with thread to American standard that has no sealing ring. Hence the gas losses are rather high and the bottles need to be replaced in regular intervals (Figure 7). The team minimized N-gas loss by decreasing N-gas flow. However, decreasing N-gas flow randomly shifted open-close He chamber operating time. Currently, one nitrogen gas bottle can be used to analyse maximum 200 samples. For long-term solution, using purified compressed air instead of N₂ and changing valve were suggested to decrease operation cost. Hence, the workshop participants were trained to check gas supplying and safety regulations before start analysing the samples.

The loading of the autosampler and programming of a sequence table with up to 50 samples was elaborated with the workshop participants, they were trained in both the sample transfer to the autosampler, use of the autosampler placing, and the maintenance to remove particles and ensure a proper use (Figure 8).

The workshop participants were creating a sequence table for running a set of samples. The relevant information that needs to be filled in the table and the settings conducted to start a run, on the laptop and EA device. Also the use a C/N list containing the exact weights from the balance to be transferred into the ChemStation sequence is a useful prerequisite for simpler calculation purpose (Figure 9). To prepare pure N standards and figure out the limit of detection with the new device setting N-standards were prepared from NH₄Cl solution in the UGM lab for elementary measurements (Figure 9).

For routine analyses not only samples reference calibration gas supply and the single steps of running the device are relevant but also the replacement of catalyst after about 500 samples, and the regular exchange of the water trap. Hence, quartz tube with catalyst, were un-mounted with the workshop participants to get them trained in the replacement of the quartz tube, and how to mount and unmounts in the EA device. A detailed explanation of how the quartz tubes are filled with new catalyst was demonstrated (Figure 10). The workshop also included the replacement of the water trap and a discussion on the timing and the appropriate storage and disposal of reagents (Figure 10). Besides training on replacement of catalysts and water trap chemicals a local supplier for consumable supplied was checked to ensure continued operation of the device.

The teams elaborated a detailed laboratory guideline with visual explanation and a short standard operational procedure for the operation of the device from the start into the standby mode into run-routine, and also from the run routine into the standby mode for gas saving conditions, as well as to full shut down of the device, if there are no more samples for analyses or a lack of supplies.

The research team has experiences that supply of material can take weeks to months, for chemicals and gases.

We assume that UGM workshop participants are well trained to conduct sample analyses with appropriate standardization procedures, and are able to interpret results. The systematic analyses of the samples now processed in UGM and statistical evaluation of the entire dataset would provide the prerequisite for common publications in a peer-reviewed journal.

Further, the measurements of spectroscopic measurements of NH₄ were again introduced, but this time to implement them for plate read spectrophotometers. This is not only of high relevance as a source for plant nitrogen nutrition, but together with NH₄OAc it can be used for the determination of the cation exchange capacity (CEC), by replacing the mineral sorption sites with NH₄. This is a method that is routinely applied in laboratories that do not have access to atomic absorption spectroscopy. The method indeed has to be modified to suit lab facilities available at UGM. While the soils from the field experiment in Bangka-Island have comparatively low cation exchange capacity the amendments applied are key to (i) regulate the soil pH value (ii) increase of soil organic matter which provides the predominant source for plant nutrients (cation exchange), particularly nitrogen and phosphorus, as well as the basis to recover the structure of the degraded soils to improve plant rooting and water storage.

Publications from this project

Website stories:

• https://boku.ac.at/news/newsitem/74041
• https://tpb.tp.ugm.ac.id/id/2023/08/03/pembelajar-sepanjang-hayat-top-up-pengetahuan-dan-keterampilan-uji-karbon-nitrogen-fosfor-pada-tanaman-dan-tanah.xhtml
• https://www.unud.ac.id/en/berita-fakultas3354-Conducting-Spectrophotometer-Usage-Training-FTP-Unud-Collaborates-with-Researchers-from-Boku-University.html
• https://tpb.tp.ugm.ac.id/id/2023/08/03/sinergi-udayana-ugm-boku-untuk-keberlanjutan-pertanian-subak.xhtml
• https://ftp.unud.ac.id/posts/consistent-towards-internationalization-ftp-unud-collaborates-with-boku-university-and-ugm

Publication and manuscripts:

• Maftukhah, R; Mentler, A; Ngadisih, N; Murtiningrum, M; Hood-Nowotny, R; Gartner, M; Kral, RM; Ploszczanski, L; Mayer, H; Keiblinger KM (in review). In-situ application of local soil amendments to post-tin mining soils – effects on heavy metal concentrations in crops and soils. Ecotoxicology and environmental safety.
• Maftukhah, R.; Keiblinger, K.M.; Ngadisih, N.; Murtiningrum, M.; Kral, R.M.; Mentler, A.; Hood-Nowotny, R. Post-tin-mining agricultural soil regeneration using local organic amendments improve nitrogen fixation and uptake in legume-cassava intercropping system. Land 2023, 12(5), 1107; https://doi.org/10.3390/land12051107.
• Maftukhah, R.; Kral, R.M.; Mentler, A.; Ngadisih, N.; Murtiningrum, M.; Keiblinger, K.M.; Gartner, M.; Hood-Nowotny, R. Post-Tin-Mining Agricultural Soil Regeneration Using Local Resources, Reduces Drought Stress and Increases Crop Production on Bangka Island, Indonesia. Agronomy 2023, 13, 50. https://doi.org/10.3390/agronomy13010050

Conferences (presentation and poster):

• Sae-Tun O, Maftukhah R, Ngadisih, Bodner G, Mentler A, Hood-Nowotny R, Keiblinger K. Impacts of biocharon boosting biological nitrogen fixation and remediating heavy metal uptake in ex-tin mining areas. BiocharDay No 6, Vienna, September 21, 2023
• Maftukhah R, Mentler A, Ngadisih N, Murtiningrum M, Kral R, Gartner M, Hood-Nowotny R, Keiblinger K. Trade-offs between nitrogen fixation and heavy metal accumulation in a cassava-legume intercropping system on post-tin mining soils amended with local organic amendments Tropentag 2023: Competing pathways for equitable food systems transformation: trade-offs and synergies September 20 – 22, 2023
• Maftukhah, R.; Kral, R.M.; Mentler, A.; Ngadisih, N.; Murtiningrum, M.; Keiblinger, K.M.; Gartner, M.; Hood-Nowotny, R. Post-tin-mining agricultural soil regeneration using local organic amendments improve nitrogen fixation in legume-cassava cropping system on Bangka Island, Indonesia. [EGU General Assembly 2023, Vienna, AUSTRIA, April 23 – 28, 2023] (online)
• Maftukhah, R; Mentler, A; Ngadisih, N; Murtiningrum, M; Hood-Nowotny, R; Gartner, M; Kral, RM; Keiblinger, KM (2022): Sustainable management of a tropical post-tin mining soil – Crop yields and heavy metal concentrations as affected by soil local amendments, [Goldschmidt 2022, Hawaii, USA (hybrid), July 10-15, 2022]
• Maftukhah, R; Mentler, A; Ngadisih, N; Murtiningrum, M; Hood-Nowotny, R; Gartner, M; Kral, RM; Keiblinger, KM (2022): Sustainable management of post-tin mining soils – soil amendment effects on heavy metals concentrations in agricultural crops [ICOSEAT 2022, Bangka, Indonesia (hybrid), July 21-23, 2022]
• Maftukhah, R; Kral, RM; Mentler, A; Ngadisih, N; Murtiningrum, M; Keiblinger KM; Gartner, M; Hood-Nowotny, R (2022): Sustainable management of post-tin mining soils – Evaluation of local soil amendments on crop yield and drought resistance [ICOSEAT 2022, Bangka, Indonesia (hybrid), July 21-23, 2022]
• Maftukhah, R; Mentler, A; Ngadisih, N; Murtiningrum, M; Hood-Nowotny, R; Gartner, M; Kral, RM; Keiblinger, KM (accepted): Charcoal for sustainable soil remediation – soil amendment effects on heavy metals concentrations in agricultural crops [Big Biochar day No. 5, Tulln an der Donau, Austria, September 15, 2022]

Video documentation:

https://www.youtube.com/watch?v=S1zBbiJt11w