Appropriate chamber deployment time for separate quantification of CH4 emissions via plant and ebullition from rice paddies using a modified closed-chamber method

A modified closed-chamber method for estimating total, plant-mediated, and bubbling (ebullition) emissions of CH4 from rice paddies has been developed to use high-time-resolution CH4 concentration data (~ 1 Hz) obtained by a spectroscopic mobile gas analyzer. Here we aimed at determining an appropriate minimum time length of chamber closure for accurate flux measurement by investigating 3255 datasets obtained from a 2-year field survey. To investigate the minimum time length for each chamber measurement, we generated a series of datasets from each measurement: by setting the hypothetical termination time of the chamber closure ahead in 1-min intervals, we obtained various chamber CH4 concentration time series with different durations of chamber closure, and separately estimated CH4 emissions via rice plants and bubbling from each. The estimated flux was sensitive to time length with short closure times, but became less sensitive with longer closure. We defined the minimum time length at which the difference in estimated flux between adjacent time windows was small enough (< 10% of plant-mediated emission). The estimated minimum time length differed from one measurement to another, but 10 min was sufficient for > 99% of cases. Detailed analysis showed a positive correlation between minimum time length and frequency of bubbling events; the time length needed to be longer as bubbling events became more frequent. From this relationship, we computed the appropriate chamber-duration time as a function of bubbling frequency. In the absence of ebullition, 4–5 min was sufficient, but as the bubbling frequency increased to 2.5 times per minute 15–20 min was necessary for accurate pathway-dependent flux measurements.

Quantifying soil denitrification in situ from depth profiles of 15N labelled denitrification products by diffusion-reaction modelling

&lt;p&gt;Common field methods for measuring soil denitrification in situ include monitoring the accumulation of &lt;sup&gt;15&lt;/sup&gt;N labelled N&lt;sub&gt;2&lt;/sub&gt; and N&lt;sub&gt;2&lt;/sub&gt;O evolved from &lt;sup&gt;15&lt;/sup&gt;N labelled soil nitrate pool in soil surface chambers. Bias of denitrification rates derived from chamber measurements results from subsoil diffusion of &lt;sup&gt;15&lt;/sup&gt;N labelled denitrification products, but this can be corrected by diffusion modeling (Well et al., 2019). Moreover, precision of the conventional &lt;sup&gt;15&lt;/sup&gt;N gas flux method is low due to the high N&lt;sub&gt;2&lt;/sub&gt; background of the atmosphere. An alternative to the closed chamber method is to use concentration gradients of soil gas to quantify their fluxes (Maier &amp;&amp;#160; Schack-Kirchner, 2014). Advantages compared to the closed &amp;#160;chamber method include the facts that (i) time consuming work with closed chambers is replaced by easier sampling of soil gas probes, (ii) depth profiles yield not only the surface flux but also information on the depth distribution of gas production and (iii) soil gas concentrations are higher than chamber gas concentration, resulting in better detectability of &lt;sup&gt;15&lt;/sup&gt;N-labelled denitrification products. Here we use this approach for the first time to evaluate denitrification rates derived from depth profiles of &lt;sup&gt;15&lt;/sup&gt;N labelled N&lt;sub&gt;2&lt;/sub&gt; and N&lt;sub&gt;2&lt;/sub&gt;O in the field by closed chamber measurements published previously (Lewicka-Szczebak et al., 2020).&lt;/p&gt;&lt;p&gt;We compared surface fluxes of N&lt;sub&gt;2&lt;/sub&gt; and N&lt;sub&gt;2&lt;/sub&gt;O from &lt;sup&gt;15&lt;/sup&gt;N labelled microplots using the closed chamber method. Diffusion&amp;#8211;based soil gas probes (Schack-Kirchner et al., 1993) were used to sample soil air at the end of each closed chamber measurement. A diffusion-reaction model (Maier et al., 2017) will be &amp;#160;used to fit measured and modelled concentrations of &lt;sup&gt;15&lt;/sup&gt;N labelled N&lt;sub&gt;2&lt;/sub&gt; and N&lt;sub&gt;2&lt;/sub&gt;O. Depth-specific values of denitrification rates and the denitrification product ratio will be obtained from best fits of depth profiles and chamber accumulation, taking into account diffusion of labelled denitrification products to the subsoil (Well et al., 2019).&lt;/p&gt;&lt;p&gt;Depending on the outcome of this evaluation, the gradient method could be used for continuous monitoring of denitrification in the field based on soil gas probe sampling. This could replace or enhance current approaches by improving the detection limit, facilitating sampling and delivering information on depth-specific denitrification. &amp;#160;&lt;/p&gt;&lt;p&gt;References:&lt;/p&gt;&lt;p&gt;Lewicka-Szczebak D, Lewicki MP, Well R (2020) N2O isotope approaches for source partitioning of N2O production and estimation of N2O reduction &amp;#8211; validation with the 15N gas-flux method in laboratory and field studies. Biogeosciences, &lt;strong&gt;17&lt;/strong&gt;, 5513-5537.&lt;/p&gt;&lt;p&gt;Maier M, Longdoz B, Laemmel T, Schack-Kirchner H, Lang F (2017) 2D profiles of CO2, CH4, N2O and gas diffusivity in a well aerated soil: measurement and Finite Element Modeling. Agricultural and Forest Meteorology, &lt;strong&gt;247&lt;/strong&gt;, 21-33.&lt;/p&gt;&lt;p&gt;Maier M, Schack-Kirchner H (2014) Using the gradient method to determine soil gas flux: A review. Agricultural and Forest Meteorology, &lt;strong&gt;192&lt;/strong&gt;, 78-95.&lt;/p&gt;&lt;p&gt;Schack-Kirchner H, Hildebrand EE, Wilpert KV (1993) Ein konvektionsfreies Sammelsystem f&amp;#252;r Bodenluft. Zeitschrift Fur Pflanzenernahrung Und Bodenkunde, &lt;strong&gt;156&lt;/strong&gt;, 307-310.&lt;/p&gt;&lt;p&gt;Well R, Maier M, Lewicka-Szczebak D, Koster JR, Ruoss N (2019) Underestimation of denitrification rates from field application of the N-15 gas flux method and its correction by gas diffusion modelling. Biogeosciences, &lt;strong&gt;16&lt;/strong&gt;, 2233-2246.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;

Reuse of Pineapple Residue in Philippine Agriculture: determination of the net ecosystem C balance for a CAM plant in a pot-scale experiment

&lt;p&gt;The Philippines is one of the world&amp;#8217;s leading producers of pineapples, wherein production is comprised mostly of small family farms that are less than 2 hectares in size. As by-product, they generate a large amount of plant residues (e.g., crowns and stems) that are commonly left at the edge of the field. This practice releases substantial amount of greenhouse gas (GHG) emissions and neglects the potential value of pineapple residue. Enabling a waste treatment by returning them to the field through incorporation or mulching holds the potential to maintain soil fertility, reduce climate impact, secure yield stability, and achieving a high resource efficiency by closing material cycles locally. It may also increase soil organic carbon stock (SOC) and reduce greenhouse gas (GHG) emissions. To date, however, the knowledge about this is still very sparse.&lt;/p&gt;&lt;p&gt;The rePRISING project aims to demonstrate that returning pineapple residue either through mulching or incorporation to the field may help promote the closing of nutrient-cycles (C/N/P/K) locally, thus helping to increase soil fertility and soil C sequestration, while reducing GHG emissions.&lt;strong&gt; &lt;/strong&gt;Within the project, the recycling of pineapple residue together with various local organic and inorganic amendments will be studied during a two-year field experiment using the manual closed chamber method. The field study will be supplemented by pot-scale greenhouse and incubation experiments, used inter alia to determine baseline GHG emissions and carbon budgets of pineapple cultivation systems and residue treatments.&lt;/p&gt;&lt;p&gt;Here we present first results of a pot experiment performed during winter 2020-2021 used to develop a suitable procedure for the in-situ determination of dynamic net ecosystem C balances (NECB) for pineapple cultivation systems. This will be further utilized for upcoming field study. This is challenging in so far as pineapple plants use the Crassulacean acid metabolism (CAM photosynthesis) and the manual closed chamber method has not yet been applied to determine NECB from CAM plants.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Keywords: &lt;/strong&gt;nutrient-cycling, carbon sequestration, greenhouse gas (GHG) emissions, pineapple residue, climate change mitigation&lt;/p&gt;

Intensive Rain Hampers the Effectiveness of Nitrification Inhibition in Controlling N2O Emissions from Dairy Slurry-Fertilized Soils

Nitrification inhibitors have been proposed as a tool to mitigate nitrous oxide (N2O) emissions from agriculture, which are caused mainly by fertilization. The nitrification inhibitor 3,4-Dimethylpyrazole phosphate (DMPP) was tested in a winter rapeseed field after dairy slurry application in Central Estonia. N2O emissions were monitored using the closed chamber method. Soil and leachate chemical parameters were also analyzed. N2O emissions increased from pre-slurry application values of 316 and 264 µg m−2 h−1 for the control and treatment plot, respectively, to maximum values of 3130.71 and 4834 µg m−2 h−1, with cumulative emissions during the study period of 12.30 kg ha−1 for the control plot and 17.70 kg ha−1 for the treatment plot. The intense precipitation period that began with the application of the slurry resulted in changes in soil moisture and water-filled pore space (WFPS), modifying the nitrification/denitrification balance. Positive significant correlations (p = 0.016 and p = 0.037, for the control and treatment plot, respectively) were found between N2O fluxes and WFPS. Future studies should consider the role of nitrifier and denitrifier communities in order to better assess in-field nitrification inhibitor effectiveness.

Pendugaan Emisi CO2 dari Lahan Gambut dengan Menggunakan Model Artificial Neural Network (ANN)

Peatlands are the most efficient carbon sinks in large volumes. Peatland clearance makes CO2 emissions released into the air. a reference of Carbon emission had a great value compared with the results of carbon emissions measurement conducted by Indonesian researchers and academics. This study aims to Conduct a continuous estimation of CO2 emissions from peatlands over a long period of time, analyze the influence of the biophysical environment on CO2 emissions and obtain CO2 emissions based on measurements of biophysical environmental parameters using ANN model. The CO2 emissions measurements were performed by closed chamber method using Licor LI-8100 for 60 days. Biophysical environmental parameter measurements are also installed simultaneously. Biophysical environmental parameters measured include soil temperature, soil moisture and water table depth. The results showed that CO2 emissions reached 59.82 TonCO2 / ha / year with carbon emissions of 16.314 TonC / ha / year. Peatland CO2 emissions are influenced by environmental parameters of peat biophysics. Calculations using the ANN model obtained the highest correlation of R2 = 0.5545 which shows that the calculation of ANN model with measurement Emission has a high enough correlation and can be used as a reference to estimated peat CO2 peatland in Padang Island. Abstrak Lahan gambut merupakan penyimpan karbon yang paling efisien dalam jumlah besar. Pembukaan lahan gambut mengakibatkan emisi CO2 terlepas ke udara. Data emisi karbon yang menjadi rujukan memiliki nilai yang lebih besar daripada hasil pengukuran emisi karbon yang dilakukan oleh peneliti dan akademisi Indonesia. Penelitian ini bertujuan untuk Melakukan estimasi emisi CO2 dari lahan gambut secara kontinyu dalam periode waktu panjang, Menganalisis pengaruh lingkungan biofisik terhadap emisi CO2 dari lahan gambut dan Mendapatkan dugaan emisi CO2 dari lahan gambut berdasarkan hasil pengukuran parameter lingkungan biofisik dengan menggunakan model ANN. Pengukuran emisi karbon dilakukan dengan metode closed chamber menggunakan Licor LI-8100 selama 60 hari. Pengukuran parameter lingkungan biofisik juga diinstal secara bersamaan dengan pengukuran emisi CO2. Parameter lingkungan biofisik yang diukur meliputi temperatur tanah, kelembaban tanah, kedalaman water table. Hasil penelitian menunjukkan bahwa emisi CO2 lahan gambut mencapai 59.82 TonCO2/ha/tahun dengan emisi karbon adalah 16.314 TonC/ha/tahun . Emisi CO2 dipengaruhi oleh parameter lingkungan biofisik gambut yaitu suhu tanah, kelembaban tanah dan kedalaman water table. Perhitungan menggunakan model ANN diperoleh korelasi tertinggi sebesar R2 = 0.5545 yang menunjukkan bahwa hasil perhitungan model ANN dengan Emisi pengukuran memiliki korelasi yang cukup tinggi dan bisa dijadikan sebagai acuan dalam mengestimasi CO2 lahan gambut Pulau Padang.

Nonvolcanic Carbon Dioxide Emission at Continental Rifts: The Bublak Mofette Area, Western Eger Rift, Czech Republic

This study presents the results of gas flux measurements of cold, mantle-derived CO2 release at the Bublák mofette field (BMF), located inside of the N-S directed Počátky Plesná fault zone (PPFZ). The PPFZ is presently seismically active, located in the eastern part of the Cheb Basin, western Eger Rift, Central Europe. The goal of the work was to identify the linkage between tectonics and gas flux. The investigated area has a size of 0,43 km2 in which 1.115 locations have been measured. Besides classical soil CO2 gas flux measurements using the closed chamber method (West Systems), drone-based orthophotos were used in combination with knowledge of plant zonation to find zones of high degassing in the agriculturally unused part of the BMF. The highest observed soil CO2 gas flux is 177.926,17 g m-2 d-1, and the lowest is 0,28 g m-2 d-1. Three statistical methods were used for the calculation of the gas flux: arithmetic mean, kriging, and trans-Gaussian kriging. The average CO2 soil degassing of the BMF is 30 t d-1 for an area of 0,43 km2. Since the CO2 soil degassing of the Hartoušov mofette field (HMF) amounts to 23 t d-1 for an area of 0,35 km2, the average dry degassing values of the BMF and HMF are in the same magnitude of order. The amount of CO2 flux from wet mofettes is 3 t d-1 for the BMF and 0,6 t d-1 for the HMF. It was found that the degassing in the BMF and HMF is not in accordance with the pull-apart basin interpretation, based on the direction of degassing as well as topography and sediment fill of the suggested basins. En-echelon faults inside of the PPFZ act as fluid channels to depth (CO2 conduits). These structures inside the PPFZ show beginning faulting and act as tectonic control of CO2 degassing.