Does agricultural practices impact the quantity and the forms of organic carbon stored in cultivated soils of the Senegal groundnut basin? A Rock-Eval approach

Author(s):  
Oscar Pascal Malou ◽  
David Sebag ◽  
Patricia Moulin ◽  
Tiphaine Chevallier ◽  
Yacine Badiane Ndour ◽  
...  

<p>Soil organic carbon (SOC) is a key element in the functioning of agrosystems. It ensures soil quality and productivity of cultivated systems in the Sahelian region. This study uses Rock-Eval pyrolysis to examine how cultural practices impact SOC quantity and quality of cultivated sandy soils in the Senegal groundnut basin. Such thermal analysis method provides cost-effective information on SOC thermal stability that has been shown to be qualitatively related to SOC biogeochemical stability. Soils were sampled within 2 villages agricultural plots representative of local agricultural systems and for local preserved areas. Total SOC concentrations ranged from 1.8 to 18.5 g.kg<sup>-1</sup> soil (mean ± standard deviation: 5.6 ± 0.4 g.kg<sup>-1</sup> soil) in the surface layer (0-10 cm) and from 1.5 to 11.3 g.kg<sup>-1</sup> soil (mean ± standard deviation: 3.3 ± 0.2 g.kg<sup>-1</sup> soil) in 10-30 cm deep layer. SOC of cultivated soils significantly (p-value < 0.0001) decreased according to treatments in the following order: +organic wastes > +manure > +millet residues > no input. Our results show that the quantity and the quality of SOC are linked to each other and both depend on land-use and agricultural practices, especially the nature of organic inputs. This correlation is very strong in the tree plantation (R² = 0.98) and in the protected shrubby savanna (R<sup>²</sup> = 0.97). It remains important for cultivated soils receiving organic wastes (R² = 0.82), manure (R<sup>²</sup> > 0.75), or millet residues (R<sup>2</sup> = 0.91) but it’s no more significant in no-input situations. The Rock-Eval based indexes were depicted in a I/R diagram that illustrate the level of SOC stabilization and plotted against comparable results from literature. The Senegalese sandy soils have thermal signatures showing an inversion of the I and the R indexes compared to data from the literature and highlighting SOC stabilization as a function of soil depth. Indeed, the studied soils were characterized by a more abundant refractory pool (A5 which ranged from 7.7 to 21.3 % in 0-10 cm layer and from 12.5 to 24.3 % in 10-30 cm, respectively) compared to other tropical soils. The SOC in these sandy soils while positively affected by organic inputs is dominated by labile forms that mineralize quickly which is excellent for the needs of productivity of these agrosystems but not for mitigation of climate change.</p><p><strong>Keywords:</strong> Soil organic carbon; Organic inputs; Thermal analysis; Agrosystems; West Africa</p>

2020 ◽  
Author(s):  
Amicie Delahaie ◽  
Pierre Barré ◽  
Lauric Cécillon ◽  
François Baudin ◽  
Camille Resseguier ◽  
...  

<p>The term Organic Waste Products (OWPs) encompasses a wide range of byproducts such as manure, sewage sludge or green waste compost. The use of OWPs impacts soil quality and functioning, agricultural yields, carbon (C) sequestration, biogeochemical cycles of nutrients like nitrogen (N) or phosphorus, and organic matter (OM) dynamics. These impacts likely depend on the considered OWP.</p><p>Taking advantage of 3 mid to long-term experimental trials (6 to 20 years) located in the Northern part of France (Paris region; Brittany; Alsace), we investigated the impact of 16 different OWPs on C content and stability. To do so, surface soil samples from replicated plots amended with the different OWPs used either alone or in addition with mineral N fertilization and appropriated control treatments were analyzed using Rock-Eval 6® thermal analyses. Samples taken up at the onset of the experiment and after 6, 18 and 20 years for the 3 sites respectively were analyzed. It resulted in the analyses of 248 different samples whose Rock-Eval 6® (RE6) signature can be used as a proxy for soil organic carbon (SOC) biogeochemical stability. In particular, we determined 2 RE6 parameters that were related to SOC biogeochemical stability in previous studies (e.g. Barré et al., 2016): HI (the amount of hydrogen-rich effluents formed during the pyrolysis phase of RE6; mgCH.g<sup>-1</sup> SOC), and T50 CO<sub>2</sub> oxidation (the temperature at which 50% of the residual organic C was oxidized to CO<sub>2</sub> during the RE6 oxidation phase; °C). We also computed the amount of centennially stable SOC from RE6 parameters using the model developed in Cécillon et al. (2018).  </p><p> </p><p>Our results showed that no clear effect of OWPs addition can be established for the youngest site (6 years). On the contrary, OWPs amendments had a clear effect on SOC quantity and quality at the sites having experienced 18 and 20 years of OWPs addition. For these sites, OWPs amendments increased SOC content, decreased SOC thermal stability (T50 CO<sub>2</sub> oxidation) and increased the Rock-Eval 6® Hydrogen Index (HI) compared to control plots. OWPs amendments tended to increase slightly the amount of centennially stable SOC at the sites having experienced 20 years of repeated OWPs application. Our results suggest that if OWPs addition does increase SOC content, at least in the long run, the majority of this additional SOC is labile and may be quickly lost if OWPs additions are stopped.</p><p> </p><p>References:</p><p>Barré P., Plante A.F., Cécillon L., Lutfalla S., Baudin F., Bernard S., Christensen B.T., Eglin T., Fernandez J.M., Houot S., Kätterer T., Le Guillou C., Macdonald A., van Oort F. & Chenu C. (2016) The energetic and chemical signatures of persistent soil organic matter. Biogeochemistry, 130: 1-12.</p><p>Cécillon L., Baudin F., Chenu C., Houot S., Jolivet R., Kätterer T., Lutfalla S., Macdonald A.J., van Oort F., Plante A.F., Savignac F., Soucémarianadin L.N. & Barré P. (2018) A model based on Rock-Eval thermal analysis to quantify the size of the centennially persistent organic carbon pool in temperate soils. Biogeosciences, 15, 2835-2849.</p>


2020 ◽  
Author(s):  
Pierre Barré ◽  
Laure Soucémarianadin ◽  
Baudin François ◽  
Chenu Claire ◽  
Bent Christensen ◽  
...  

<p>The organic carbon reservoir of soils is a key component of climate change, calling for an accurate knowledge of the residence time of soil organic carbon (SOC). Existing proxies of the labile SOC pool such as particulate organic carbon or basal respiration tests are time consuming and unable to consistently predict SOC mineralization over years to decades. Similarly, models of SOC dynamics often yield unrealistic values of the size of SOC kinetic pools. Rock-Eval® 6 (RE6) thermal analysis of bulk soil samples has recently been shown to provide useful and cost-effective information regarding the long-term in-situ decomposition of SOC. The objective of this study was to design a method based on RE6 indicators to assess for a given soil, the proportion of SOC that will be mineralized in the coming 20 years.</p><p>To do so, we needed samples ready to be analyzed using RE6 with a known proportion of SOC mineralized in 20 years. We used archived soil samples from 4 long-term bare fallows and 8 C<sub>3</sub>/C<sub>4</sub> chronosequences. For each sample, the value of bi-decadal SOC mineralization was obtained from the observed SOC dynamics of its long-term bare fallow plot or the calculated C<sub>3</sub>-derived SOC decline following the conversion to C<sub>4</sub> plants. Those values ranged from 0.3 to 14.3 gC·kg<sup>−1</sup> (concentration data), representing 8.6 to 52.6% of total SOC (proportion data). All samples were analyzed using RE6 and simple linear regression models were used to predict bi-decadal SOC loss (concentration and proportion data) from 4 RE6 parameters: 1) HI (the amount of hydrogen-rich effluents formed during the pyrolysis phase of RE6; mgCH.g<sup>-1</sup> SOC), 2) OI<sub>RE6</sub> (the O recovered as CO and CO<sub>2</sub> during the pyrolysis phase of RE6; mgO<sub>2</sub>.g<sup>-1</sup> SOC), 3) PC/SOC (the amount of organic C evolved during the pyrolysis phase of RE6; % of total SOC) and 4) T50 CO<sub>2</sub> oxidation (the temperature at which 50% of the residual organic C was oxidized to CO<sub>2</sub> during the RE6 oxidation phase; °C).</p><p>The RE6 HI parameter yielded the best predictions of bi-decadal SOC mineralization, for both concentration and proportion data. PC/SOC and T50 CO<sub>2</sub> oxidation parameters also yielded significant regression models. The OI<sub>RE6</sub> parameter was not a good predictor of bi-decadal SOC loss, with non-significant regression models. The results showed that SOC chemical composition (HI is a proxy for SOC H/C ratio), and to a lesser degree SOC thermal stability, are related to bi-decadal SOC dynamics. The RE6 thermal analysis method can therefore provide a quantitative and accurate estimate of SOC biogeochemical stability.</p>


2021 ◽  
Author(s):  
Lauric Cécillon ◽  
François Baudin ◽  
Claire Chenu ◽  
Bent T. Christensen ◽  
Uwe Franko ◽  
...  

Abstract. Partitioning soil organic carbon (SOC) into two kinetically different fractions that are centennially stable or active is key information for an improved monitoring of soil health and for a more accurate modelling of the carbon cycle. However, all existing SOC fractionation methods isolate SOC fractions that are mixtures of centennially stable and active SOC. If the stable SOC fraction cannot be isolated, it has specific chemical and thermal characteristics that are quickly (ca. 1 h per sample) measureable using Rock-Eval® thermal analysis. An alternative would thus be to (1) train a machine-learning model on the Rock-Eval® thermal analysis data of soil samples from long-term experiments where the size of the centennially stable and active SOC fractions can be estimated, and (2) apply this model on the Rock-Eval® data of unknown soils, to partition SOC into its centennially stable and active fractions. Here, we significantly extend the validity range of the machine-learning model published by Cécillon et al. [Biogeosciences, 15, 2835–2849, 2018, https://doi.org/10.5194/bg-15-2835-2018], and built upon this strategy. The second version of this statistical model, which we propose to name PARTYSOC, uses six European long-term agricultural sites including a bare fallow treatment and one South American vegetation change (C4 to C3 plants) site as reference sites. The European version of the model (PARTYSOCv2.0EU) predicts the proportion of the centennially stable SOC fraction with a conservative root-mean-square error of 0.15 (relative root-mean-square error of 0.27) in a wide range of agricultural topsoils from Northwestern Europe. We plan future expansions of the PARTYSOC global model using additional reference soils developed under diverse pedoclimates and ecosystems, and we already recommend the application of PARTYSOCv2.0EU in European agricultural topsoils to provide accurate information on SOC kinetic pools partitioning that may improve the simulations of simple models of SOC dynamics.


2020 ◽  
Vol 301 ◽  
pp. 107030
Author(s):  
Oscar Pascal Malou ◽  
David Sebag ◽  
Patricia Moulin ◽  
Tiphaine Chevallier ◽  
Ndeye Yacine Badiane-Ndour ◽  
...  

2021 ◽  
Vol 14 (6) ◽  
pp. 3879-3898
Author(s):  
Lauric Cécillon ◽  
François Baudin ◽  
Claire Chenu ◽  
Bent T. Christensen ◽  
Uwe Franko ◽  
...  

Abstract. Partitioning soil organic carbon (SOC) into two kinetically different fractions that are stable or active on a century scale is key for an improved monitoring of soil health and for more accurate models of the carbon cycle. However, all existing SOC fractionation methods isolate SOC fractions that are mixtures of centennially stable and active SOC. If the stable SOC fraction cannot be isolated, it has specific chemical and thermal characteristics that are quickly (ca. 1 h per sample) measurable using Rock-Eval® thermal analysis. An alternative would thus be to (1) train a machine-learning model on the Rock-Eval® thermal analysis data for soil samples from long-term experiments for which the size of the centennially stable and active SOC fractions can be estimated and (2) apply this model to the Rock-Eval® data for unknown soils to partition SOC into its centennially stable and active fractions. Here, we significantly extend the validity range of a previously published machine-learning model (Cécillon et al., 2018) that is built upon this strategy. The second version of this model, which we propose to name PARTYSOC, uses six European long-term agricultural sites including a bare fallow treatment and one South American vegetation change (C4 to C3 plants) site as reference sites. The European version of the model (PARTYSOCv2.0EU) predicts the proportion of the centennially stable SOC fraction with a root mean square error of 0.15 (relative root mean square error of 0.27) at six independent validation sites. More specifically, our results show that PARTYSOCv2.0EU reliably partitions SOC kinetic fractions at its northwestern European validation sites on Cambisols and Luvisols, which are the two dominant soil groups in this region. We plan future developments of the PARTYSOC global model using additional reference soils developed under diverse pedoclimates and ecosystems to further expand its domain of application while reducing its prediction error.


2018 ◽  
Vol 117 ◽  
pp. 108-116 ◽  
Author(s):  
Laure Soucémarianadin ◽  
Lauric Cécillon ◽  
Claire Chenu ◽  
François Baudin ◽  
Manuel Nicolas ◽  
...  

2019 ◽  
pp. 217-310 ◽  
Author(s):  
Jenifer L. Yost ◽  
Alfred E. Hartemink

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