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Chapitre 3 : Etude du devenir des Mafor dans les sols – Minéralisation et effet sur la stabilité

3.2. Influence des caractéristiques biochimiques des Mafor sur la minéralisation du

3.2.3. Results Modelling of the model compartments

For all OM compartments, initializations were achieved using the data obtained from the laboratory measurements described in part 2 and values are summarized in Tableau 24.

Tableau 24 : Initial compartments of the CANTIS model.

MAN: Cattle manure; ADMAN: Solid phase of the anaerobic digestate of MAN; CMAN: Compost of MAN;

ADBIO: Solid phase of the anaerobic digestate of biowaste; CBIO: compost of biowaste. EOM: Exogenous organic matter; SOLsoil: Soluble fraction of soil organic matter; HOM: Humified soil organic matter; ZYB:

Zymogenous microbial biomass; Autochthon microbial biomass; HEM: Hemicellulose-like fraction of EOM;

CEL: Cellulose-like fraction of EOM; LIC: Lignin and cutin-like fraction of EOM; SOLf: Soluble fraction of EOM with a fast degradation rate; SOLs: Soluble fraction of EOM with a slow degradation rate.

The initial C of HOM C was provided by the soil TOC, of 11.8 dry soil but its C/N ratio of 9.7 was fitted by minimizing the RMSE on the mineralization curves of the control (soil without EOM).

The initial SOLsoil C content of 120 dry soil was evaluated from the C mineralized in the first days of the control incubation, before the cumulated CO2 produced by the control achieve a linear phase. It thus corresponded to the soil labile C. It C/N ratio was then fitted by minimizing the RMSE of the mineralization curves of the control treatment (soil without EOM).

Initial compartment Unit MAN ADMAN CMAN ADBIO CBIO

Amount of EOM added mg 4000 4000 4000 4000 4000

Amount of C in SOLsoil mg 120 120 120 120 120

Amount of C in HOM mg 11780 11780 11780 11780 11780

C/N ratio of SOLsoil - 20 20 20 20 20

C/N ratio of HOM - 9.7 9.7 9.7 9.7 9.7

Amount of C in ZYB mg 47.4 48.5 43.6 42.4 52.0

Amount of C in AUB mg 142.2 145.5 130.8 127.2 155.9

C/N ratio of ZYB - 6.7 6.7 6.7 6.7 6.7

C/N ratio of AUB - 10 10 10 10 10

Amount of N-NH4

+ mg 7.2 12.6 2.4 3.8 0.9

Amount of N-NO3- mg 16.9 12.2 17.2 14.2 14.5

Proportion of HEM+CEL % TC of the EOM 46.7 47.1 25.0 45.6 29.3

Proportion of LIC % TC of the EOM 15.2 19.7 24.9 35.9 39.4

Proportion of SOLf % TC of the EOM 13.8 7.4 3.2 0.0 0.0

Proportion of SOLs % TC of the EOM 24.4 25.8 46.7 18.5 31.3

C/N ratio of HEM+CEL - 47.2 74.6 20.1 85.5 43.7

C/N ratio of LIC - 17.0 22.4 16.1 26.8 17.3

C/N ratio of SOLf - 100 100 66.7 - -

C/N ratio of SOLs - 4.1 4.4 7.8 9.7 11

176 The initial total biomass C was measured for each treatment on day 0 and was split into AUB and ZYB by considering a 3/4-1/4 ratio, as proposed by Oorts at al. (2007). The C/N of AUB and ZYB were set to 10 and 6.7 respectively, which are in the typically ranges proposed for soil microbial biomass as proposed by Kallenbach & Grandy (2011) who found that the mean C/N ratio for soil microbes was 8.6, with 70% of the values included in the 6 to 11 range.

These values also correspond to the 6.6 value proposed by Reiners (1986) for bacteria.

The initial total FOM C was set at 4000 (amount of C added to the soil by the EOM) and its N amount was calculated using the C/N of the EOM.

The biochemical fractionation of the EOM permitted to directly initialize the HEM+CEL and LIC fractions for all mixture simulations. However, the recalcitrance of the SOL fraction (SOLnd+SOLH2O) increases during the composting process (Peltre et al., 2010) and is not representative of the quickly degraded fraction (Chalhoub et al., 2013). It was proposed in a previous study conducted by Chaloub et al. (2013) to consider that water soluble C was 100 % either in SOLs or in SOLf depending on the organic products considered. We aimed in this present work, in achieving the water soluble C distribution in SOLs or SOLf based on an analytical measurements. In fact, recent studies showed that the biodegradability of the water-soluble fractions of composts was linked to the molecular weights of the water-soluble molecules (Wei et al., 2014) which in turn displayed an important evolution during composting (Tremier et al., 2014). Thus, ultrafiltration or HPLC technique may be useful in specifying the recalcitrance of the soluble fraction of EOM. The distribution of C between SOLf and SOLs was thus achieved by HPLC to estimate the size distribution of the EOM water-soluble molecules (Tremier et al., 2014). Thus, the SOLf fraction was assumed equal to the water soluble small molecules (molecular weight <1.5 kDa) whereas the high molecular weight (>1.5 kDa) water soluble molecules pertained to the SOLs compartment. This assumption was based on Janning (1998) stating that for bacterial cellular membrane diffusion, only molecules smaller than 0.0005 µm can be considered, which are approximately equivalent to a molecular weight of 1.5 kDa (Erickson, 2009). These molecules are though presumably quickly assimilated by the microbial biomass. Some 53%, 56% and 14% of the water-soluble molecules were <1.5 kDa for MAN, ADMAN and CMAN, respectively, whereas no soluble C was obtained in SOLH2O for ADBIO and CBIO. By this method, it was found that not only composts, but also raw and digested EOM, contained a SOLs compartment. However the highest values of SOLs were found in composted materials (Tableau 24).

177 Hot water extractable N is reported as a poor predictor of labile N for different EOM, including composted cattle manures (Antil et al., 2011), as found in the present experimental work. If the entire N in SOLH2O was considered to be found in the SOLf compartments, N mineralization would have been overestimated (results not shown). For all five EOM, the degraded soluble fraction is mainly composed of non-nitrogenous small molecules (ex: small carbohydrates) whereas the slowly degraded soluble fraction is mainly composed of heavy nitrogenous molecules. Peltre et al. (2010) found that recalcitrant N-containing compounds are extracted in the SOL fraction. Luxhoi et al. (2007) also found high C/N ratios (4.7x107 and 100) for the labile pool and small ones (4.8 and 15) for the recalcitrant pool when modelling the mineralization of digested and composted municipal solid waste in soil.

Laboratory analyses provided the amounts of inorganic nitrogen (NH4+ and NO3-) for each mixture (soil+EOM) and the soil (control). procedure

Tableau 25 summarizes the parameters of the model, their values and the quantification method used.

Tableau 25 : Parameters values of the CANTIS model and sources.

EOM: Exogenous organic matter; SOLsoil: Soluble fraction of soil organic matter; HOM: Humified soil organic matter; ZYB: Zymogenous microbial biomass; Autochthon microbial biomass; HEM: Hemicellulose-like fraction of EOM; CEL: Cellulose-like fraction of EOM; LIC: Lignin and cutin-like fraction of EOM; SOLf:

Soluble fraction of EOM with a fast degradation rate; SOLs: Soluble fraction of EOM with a slow degradation rate.

Parameters Description Unit Parameters value Sources

k1 Potential rate constant of HEM+CEL day-1 0.027 Chalhoub et al., 2013

k2 Potential rate constant of LIC day-1 0.0022 Chalhoub et al., 2013

k3 Potential rate constant of SOLf day-1 0.253 Chalhoub et al., 2013

k4 Potential rate constant of SOLs day-1 0.0018 Optimized

kS Potential rate constant of SOLsoil day-1 1.49 Iqbal et al., 2014

kZ Death rate constant of ZYB day-1 0.1 Iqbal et al., 2014

kA Death rate constant of AUB day-1 0.012 Optimized in the control

kH Potential rate constant of HOM day-1 0.000302 Optimized in the control

YS Assimilation yield of SOLsoil by ZYB - 0.55 Iqbal et al., 2014

YZ Assimilation yield of ZYB by ZYB - 0.55 Iqbal et al., 2014

YA Assimilation yield of AUB by AUB - 0.55 Iqbal et al., 2014

YH Assimilation yield of HOM by AUB - 0.55 Iqbal et al., 2014

HZ Humification coefficient of ZYB - 0.3 Iqbal et al., 2014

HA Humification coefficient of AUB - 0.9 Chalhoub et al., 2013

kr Retardation factor for HEM+CEL decomposition - 3.2 Iqbal et al., 2014

kaff Michaëlis-Menten factor on SOLsoil and FOM decomposition mg 0 (93 for composts) Optimized

178 Parameters for soil decomposition

The rate constant of HOM decomposition (kH) and the decomposition rate of AUB (kA) were estimated by optimization using the measured C and N mineralization for the control treatment (soil without EOM). The value for kA was found to be very close to that obtained by Garnier et al. (2003) (0.0108 d-1) and Chalhoub et al. (2013) (0.02 d-1) but was higher than that obtained by Iqbal et al. (2014) (1.8.10-3 d-1) despites the fact that the later study was also performed on a similar loamy cultivated soil with a low organic C content (0.95%).

However, this parameter may be linked to the soil microbial communities and is thus expected to vary between soils. The optimized kH value was of 3.02x10-4 d-1 (Tableau 25), which fell within the range proposed by Iqbal et al. (2014) (1.52x10-4 d-1) and Chalhoub et al. (2013) (6x10-4 d-1). The humification coefficient for AUB (HA) was taken from Chalhoub et al.


EOM decomposition parameters

Except for k4 (rate constant for SOLs decomposition), all the rate constants for the decomposition of the FOM fractions (k1, k2 and k3) were taken from Chalhoub et al. (2013) (Tableau 25). The k1 was thus set to 0.027 d-1 which is in the range of the values proposed for the cellulolytic fraction by Corbeels et al. (1999), Gignoux (2001) and Hadas & Molina (1993), respectively, of 0.02 d-1 and 0.019 to 0.038 d-1, and 0.024 d-1. The k2 coefficient was set to 2.2x10-3 d-1for LIC degradation which is lowest than the value proposed by Gignoux et al. (2001) for lignin degradation (between 0.0095 and 0.019 d-1), whereas lower values were also found in the literature, such as 1x10-5 d-1 by Trinsoutrot et al. (2000b) and 9.5x10-4 d-1 by Quemada & Cabrera (1995) for crop residues. As the degradation of LIC is very slow, the k2

coefficient is expected to depend on the duration of the incubation and thus can vary amongst studies.

The k3 coefficient was set to 0.253 d-1 for SOLf degradation (Tableau 25). Hadas et al. (2004) and Corbeels et al. (1999) found higher values for the soluble fraction degradation, respectiveley, of 0.4 d-1 and 0.8 d-1, whereas Gignoux et al. (2001) proposed smaller values for sugar degradation of 0.06305 to 0.1261 d-1. However, as the water soluble fraction is a major driver of organic substrate biodegradation during bio-treatment (composting or anaerobic digestion), the composition of the SOL fraction is subject to biochemical changes during treatment (Peltre et al., 2010; Tambone et al., 2009; Tremier et al., 2014), thus explaining differences amongst EOM. This may partly explain the high variability in soluble fraction degradation rates found in the literature.

179 As the value proposed by Chalhoub et al. (2013) for k4 (1x10-4 d-1) applied to our data lead to an underestimation of C mineralization, the k4 coefficient for SOLs was optimized, firstly for each EOM mineralization rates. Then, the mean of the obtained values for the five EOM (between 0.0008 and 0.003 d-1) was used as unique value for all five EOM (0.0018 d-1).

Microbial parameters

The four assimilation yields (YS, YZ, YA and YH), the decomposition rate of ZYB (kZ), the humification coefficient of ZYB (HZ), the rate constant of SOL decomposition (KS) and the retardation factor for the decay of HEM+CEL (kr) were taken from Iqbal et al. (2014). The kaff

coefficient was first adjusted for each EOM. As the obtained values for the two composts were very close (90 and 96, the mean value was used to perform new simulations.

The optimized kaff value was 0 for the threeother EOM, meaning that the affinity of microorganisms for the substrate was greater in the digestates and fresh manure than in the composts (microbial biomass is a limiting factor for the composts). Since composting and anaerobic digestion lead to changes in microbial communities (Franke-Whittle et al., 2014) and substrate availability, the kaff coefficient may depend on EOM type. Indeed, Gomez-Brandon et al. (2008) showed that the microbial community and the enzymes activities, such as that for cellulose, decreased in composted manure as compared to raw manure.

Furthermore, Ng et al. (2014) found that EOM type and composition influenced both microbial composition and activity. quality

The predicted C and N mineralization kinetics are presented in Figure 39 and Figure 40, and the statistics to evaluate model performance are presented in Tableau 26. The RMSE on the cumulated CO2 production ranged from 13.1 (CBIO) to 166.2 mg dry soil (ADBIO). As attested by the high Fr values, most of the CO2 measurements were predicted with an error under 15%, excepted for ADBIO (only 46 % of the predicted values fell in the measured values ±15%). The RMSE calculated on the NO3- ranged between 2.6 dry soil (CBIO) and 14.4 dry soil (ADMAN), which represented quite important errors of predictions as attested by the quite low Fr values. However the trends in NO3- were well predicted, excepted for ADMAN for which immobilization was simulated in the first days despite a net measured N mineralization.


Tableau 26: Statistics to evaluate the calibrated model.

RMSE: Root mean square error; Fr: Frequency at which the difference between the predicted value and the measured value fell within the measured value ± 15% range; MAN: Cattle manure; ADMAN: Solid phase of the anaerobic digestate of MAN; CMAN: Compost of MAN; ADBIO: Solid phase of the anaerobic digestate of biowaste; CBIO: compost of biowaste. of the biochemical fractions to the overall carbon and nitrogen mineralisation

The model calculated the contribution of each EOM fraction to the total C and N mineralization (Tableau 27).

Tableau 27: Contribution of each organic fraction to the overall C and N mineralization of the exogenous organic matters (% of C in degraded EOM).

MAN: Cattle manure; ADMAN: Solid phase of the anaerobic digestate of MAN; CMAN: Compost of MAN;

ADBIO: Solid phase of the anaerobic digestate of biowaste; CBIO: compost of biowaste; EOM: Exogenous organic matter; HEM: Hemicellulose-like fraction of EOM; CEL: Cellulose-like fraction of EOM; LIC: Lignin and cutin-like fraction of EOM; SOLf: Soluble fraction of EOM with a fast degradation rate; SOLs: Soluble fraction of EOM with a slow degradation rate.

These estimations were dependent on the hypothesis made to develop and calibrate the model.

The C mineralization rates of the HEM+CEL and LIC fractions were the same for all EOM, as assumed by Morvan and Nicolardot (2009). Considering C degradation, HEM+CEL was the major fraction contributing to C mineralization in all five EOM. However the contribution of this fraction for the composted wastes was slightly lower as compared to non-treated or digested wastes. This can be attributed to the small initial HEM+CEL content in composts (Tableau 23) and the high compost lignocellulose index which slowed HEM+CEL degradation (Equation 2). LIC contributed in small amounts in the mineralization of the EOM stemming from manure (less than 15%), but in higher extents for the EOM stemming from the biowaste (26 and 31 % for ADBIO and CBIO, respectively).

For these five EOM, the SOLs contribution was also non-negligible as 12 to 26 % of the


HEM+CEL 58 62 37 62 47 28 18 29 25 22

181 mineralization in composts as it was initially high as compared to what was observed for digestates and manure (Tableau 24). The k4 for SOLs degradation, obtained by optimization, was found closed to the one describing the degradation of the LIC fraction. This is in agreement with the idea reported by Thuriès et al. (2002) that, depending on the composting process, the degradation of the LIC fraction could occur into soluble fulvo-humic acid resistant to microbial attack. Nevertheless, the high contribution of the SOLs fraction found in the present paper is different from the result obtained by Morvan & Nicolardot (2009) who found, by separately incubating the OM fractions of different EOM in soils, that the Van Soest SOL fraction (SOLH2O+SOLnd) of a composted manure did not contribute significantly to the overall C mineralization whereas for the non-composted manure, this fraction contributed to about 20%. Since the overall decomposition of the two composts is correctly simulated, the possible overestimation of the soluble fraction contribution to the carbon mineralization for the two composts (49 and 22 % respectively for CMAN and CBIO) is managed by the introduction of the limitation coefficient kaff to account for the shift within microbial affinity for the substrate during composting. A proper validation is thus necessary for this model, by measuring the dynamics of the biochemical fractions over time and calculating the biodegradation rates of each fraction during EOM degradation in soil. A better knowledge of microbial biomass dynamics and activity during decomposition is also critical.

Considering N degradation, the SOLs was the major fraction contributing to N mineralization in the all five EOM (41 to 69 % of the mineralize N, Tableau 27), because of the low C/N ratio found in this fraction (4 to 11, Tableau 24). A high C/N ratio of up to 100 was found in SOLf, for MAN and ADMAN (Tableau 24). However, the contribution of this fraction to the overall N degradation was non negligible for MAN at 25 %, because of its high levels and its high degradation rate. Morvan & Nicolardot (2009) found that almost all inorganic nitrogen provided by manure compost mineralization came from the water soluble fraction. As opposed to the present results, they observed an important manure net N immobilization at the end of the incubation.

3.2.4. Conclusions

The objectives of the present study were to compare the mineralization rates of EOM obtained from different treatment techniques, such as raw, composted and digested, and to test the ability of the CANTIS model to accurately simulate the behavior of this wide range of EOM in soils using a unique set of parameters. The present study showed that composts are highly

182 stabilized products (low C and N mineralization) whereas digestates and fresh manure are highly mineralized in soils. The CANTIS model permitted to simulate the C and N mineralization of EOM in soils and evaluate the contribution of each EOM fraction considered as inputs of the model (soluble (fast and slow), hemicellulose, cellulose and lignin) to the overall mineralization process. Based on analytical results using the organic fractionation method derived from Van Soest’s and HPLC for the estimation of the quickly degraded SOL fraction, the CANTIS model was successfully initialized and calibrated, leading to a unique set of parameters for all five EOM. The only exception was the Michaelis-Menten coefficient for the zymogen microbial biomass (kaff), newly introduced in the model, which was found to be dependent on the EOM treatment, namely composted versus non-composted wastes.

Thus, OM characteristics directly drove the fate of soil C degradation for all five EOM.

However, the distribution of N in the SOL fraction was optimized for each EOM, meaning that the solubility of this fraction in hot water is not a criterion evaluating the N biodegradability of a highly diverse source of EOM.

Additional research is needed to achieve the complete experimental initialization of the model, including the N distribution in the SOLs and SOLf fractions. Thus, a better characterization of the compost soluble fraction is needed. In the future, the model is expected to be used as predictive tool without need of new calibrations.


The authors acknowledge the contribution of the farm and plant owners supplying the experimental wastes. We are grateful to Armelle Racapé, Delphine Clugnac and Laurette Gratteau for their technical support.

We wish to thank the Agence de l'Environnement et de la Maîtrise de l'Energie, the Région Bretagne, the Direction Générale de l’Enseignement et de la Recherche and the Natural Science and Engineering Research Council of Canada for their financial support during the project.


AFNOR. 2009. Caractérisation de la matière organique par fractionnement biochimique et estimation de sa stabilité biologique. in: Amendement organiques et supports de culture, Association Française de Normalisation. Paris, France, pp. 17.

Amlinger, F., Gotz, B., Dreher, P., Geszti, J., Weissteiner, C. 2003. Nitrogen in biowaste and yard waste compost: dynamics of mobilisation and availability - a review. European Journal of Soil Biology, 39(3), 107-116.

183 Annabi, M., Houot, S., Francou, F., Poitrenaud, M., Le Bissonnais, Y. 2007. Soil aggregate stability improvement with urban composts of different maturities. Soil Science Society of America Journal, 71(2), 413-423.

Antil, R.S., Bar-Tal, A., Fine, P., Hadas, A. 2011. Predicting Nitrogen and Carbon Mineralization of Composted Manure and Sewage Sludge in Soil. Compost Science &

Utilization, 19(1), 33-43.

Baize, D., Girard, M.C. 2008. Référenciel pédologique 2008. Quae ed. AFES, Versailles, France.

Bernal, M.P., Alburquerque, J.A., Moral, R. 2009. Composting of animal manures and chemical criteria for compost maturity assessment. A review. Bioresource Technology, 100(22), 5444-5453.

Bernal, M.P., Sanchez-Monedero, M.A., Paredes, C., Roig, A. 1998. Carbon mineralization from organic wastes at different composting stages during their incubation with soil.

Agriculture Ecosystems & Environment, 69(3), 175-189.

Chalhoub, M., Garnier, P., Coquet, Y., Mary, B., Lafolie, F., Houot, S. 2013. Increased nitrogen availability in soil after repeated compost applications: Use of the PASTIS model to separate short and long-term effects. Soil Biology & Biochemistry, 65, 144-157.

Corbeels, M., Hofman, G., Van Cleemput, O. 1999. Simulation of net N immobilisation and mineralisation in substrate-amended soils by the NCSOIL computer model. Biology and Fertility of Soils, 28(4), 422-430.

Dalal, R.C. 1998. Soil microbial biomass - what do the numbers really mean? Australian Journal of Experimental Agriculture, 38(7), 649-665.

de la Fuente, C., Alburquerque, J.A., Clemente, R., Bernal, M.P. 2013. Soil C and N mineralisation and agricultural value of the products of an anaerobic digestion system. Biology and Fertility of Soils, 49(3), 313-322.

Delcour, D., Rathouis, P., Balny, P., Guillet, M., Roussel, F. 2013. Plan d'action relatif à une meilleure utilisation de l'azote en agriculture. Ministère de l'agriculture, de l'agroalimentaire et de la forêt ; Ministère de l'écologie, du développement durable et de l'énergie.

DeNeve, S., Hofman, G. 1996. Modelling N mineralization of vegetable crop residues during

DeNeve, S., Hofman, G. 1996. Modelling N mineralization of vegetable crop residues during

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