Datos cuantitativos

REVALLIER, A.1_{, ORVAIN, M.}1_{, BISINELLA DE FARIA, A. B.}1_{, NAVES-MASCHIETTO, G.}1_{, ALBUQUERQUE, M.}1_,

HOUOT, S.2_{, HARTMAN, M.}3_{, PARTON, B.}3

1 _{Veolia Recherche & Innovation, France;} 2 _{INRA Ecosys, France;} 3 _{Colorado State University, United States of America}

INTRODUCTION

In a context of high environmental impact of fertilizer use and soil organic matter (OM) degradation, recycling nutrients and stabilizing soil OM through organic residues applications such as composts has become an essential objective of sustainable farming. However, efficient use of compost is still a challenge, due to high variability of OM mineralization that depends on its quality and on various soil and climate characteristics. Modelling and simulation of OM mineralization and its impacts on N, P and K dynamics play an important role when understanding nutrient interactions and optimizing compost spreading.

The Century model (Parton et al., 1987) describes the different OM pools dynamics in agricultural soils at monthly scale and considers pedo-climatic context and farming practices including residual organic matter additions. This study describes the modifications to Century and the validation of the results with a long-term field experiment in France.

The aim of this study is to modify, calibrate and validate Century model in order to correctly predict C, N, P and K in soil and differentiate between different compost spreading strategies for a French pedo-climatic context. MATERIAL AND METHODS

Integration of ISMO index to Century model

Century describes the dynamics of soil organic matter and nutrient cycling between 3 different pools: active, slow and passive soil organic matter (SOM). These SOM pools are supplied by structural and metabolic C, N, P and S pools. In the first study (data not published), it was noted that the effects of different composts additions on soil organic matter mineralization was not precisely predicted. To be able to differentiate between the types of amendment used, the Organic Matter Stability Index (ISMO) (Lashermes et al., 2009) of composts was integrated to Century. Century uses the ISMO to divide organic matter into the structural carbon and the slow organic carbon pools. Between ISMO of 36% to 90%, the OM going into the slow organic carbon pool is linearly proportional to the value of ISMO. Consequently, the flow going into the structural pool decreases with the increase of ISMO. In addition, it is important to predict K due to its fertilization effect and its presence in organic amendments. Therefore, the dynamics of S, initially simulated by Century, have been adapted to describe K dynamics in soil, based on the SOM mineralization and C/K ratios to describe the fluxes between different pools.

Model validation

To validate the modifications in the model, an experimental dataset provided by the long-term field experiment QualiAgro (INRA-Veolia partnership, http://www6.inra.fr/qualiagro) dedicated to compost application, was used. In the QualiAgro experiment, three types of composts and farm manure were applied every two years on a loamy soil cropped with corn and winter wheat from 1998 to 2013. Control plots (TEM) were cropped without organic amendments and half of the experimental sites were fertilized (EXPERIMENT_N) while the other part received no mineral fertilizer, leading to 10 different treatments which are replicated 4 times. Also, the ISMO value of organic amendments was measured along with soil characteristics including C, N, P and K stocks. Statistical analyses using linear regression were conducted to compare model predictions and measurements. Three different organic amendments (including municipal solid waste compost - OMR) and the control treatments were used to calibrate the model while a last treatment (compost of sludge and green waste - DVB) was used to validate the calibration.

RESULTS AND DISCUSSION

The model predictions showed strong correlations with experimental soil total organic carbon (r²=0.91) and soil total organic nitrogen stock (r²=0.90) as shown in Figure 1 for TEM_N, OMR_N and DVB_N. Also, the modified version of Century distinguished precisely the scenarios with and without amendments as well as the type of compost regarding its stabilization level.

Figure 1. Total Soil Organic Matter Carbon (A) and Nitrogen (B). Comparison among Century results and QualiAgro data for TEM_N (control plot with mineral N fertilization), OMR_N (municipal solid waste compost with mineral N fertilization) and DVB_N (sludge and green waste compost with mineral N fertilization).

Predictions of exchangeable P and K stocks in soil (data not shown) were also in accordance with the measurement values. However, more experimental data concerning total P and K are needed to improve the whole P and K dynamics in soil.

CONCLUSION

The calibration and validation of the modified Century model implemented with ISMO and K showed encouraging results for the French organic amendment scenarios. As a next step, a sensitivity analysis and more powerful calibration tools will be used to decrease the uncertainty of Century prediction. Also, the use of different calibration and validation datasets will enhance the capability of the model to predict C, N, P and K soil dynamics in various French pedo-climatic and organic amendment contexts.

Acknowledgements: The authors acknowledge INRA Ecosys for providing QualiAgro experimental data. REFERENCES

Parton, W. J., Schimel, D. S., Cole, C. V., & Ojima, D. S. (1987). Analysis of factors controlling soil organic matter levels in Great Plains grasslands. Soil Science Society of America Journal, 51(5), 1173-1179.

Lashermes, G., Nicolardot, B., Parnaudeau, V., Thuriès, L., Chaussod, R., Guillotin, M. L., ... & Tricaud, A. (2009). Indicator of potential residual carbon in soils after exogenous organic matter application. European Journal of Soil Science, 60(2), 297-310.

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