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Measuring and modelling the dynamics of carbon and nitrogen mineralization from diverse plant residues in soil – plant systems

dc.contributor.advisorWhitbread, Anthony Prof. Dr.
dc.contributor.authorNguyen, Trung Hai
dc.titleMeasuring and modelling the dynamics of carbon and nitrogen mineralization from diverse plant residues in soil – plant systemsde
dc.contributor.refereeDittert, Klaus Prof. Dr.
dc.description.abstractengNutrient cycling in the soil – plant ecosystem is an essential component of sustainable productive agricultural activities. Although during the last 20 years inorganic fertilizer have played a dominant role of nutrient supply source for plant growth, plant residues also play an important role, especially in low agricultural farming systems in developing countries. Understanding the dynamics of soil organic matter which is mainly added from plant residues plays an important role to face with several issues of both environmental and agricultural aspects. The aim of this dissertation is to explore the kinetics of carbon and nitrogen mineralization from diverse plant residues and to evaluate the performance of soil organic matter model in capturing these processes. Decomposition processes of various plant residues in this study were driven mainly by their quality and soil types rather than by residues practice management. Higher production of CO2 release was recognized in low C:N ratio, small lignin content in high soil organic carbon content. Moreover, the CO2 release increased rapidly in the first 4 weeks of incubation and reached around 40% to three fourths of total C mineralized, especial in very poor nutrient soil (N% = 0.012) it reached up to 50% only in the first weeks. For example, the cumulative CO2 – C emission from cacao and flemingia (lignin content over 20%) accounted for over 40% during 4 weeks of incubation but this figure increased to around 70% in lablab, maize and mucuna (lignin content less than 10%). The net N mineralized from plant residues profoundly influenced by the concentration of mineral N in soil and the residue quality. When applying the same residue type, the larger amount of net N min was found in sandy soil with low N concentration (7 mg N kg-1 soil) compared with clay soil (30 mg N kg-1 soil). Furthermore, under well-controlled condition, residues with overall C:N ratio lower than 27 resulted a net mineralisation and the net immobilization occurred in residues having overall C:N ratio higher than this value. Nevertheless in greenhouse condition, the net N immobilization was mainly dominant during 7 months of experiment either placed residues on the surface or mixed them with soil. The residue quality strongly influenced on the total N recovery to plant. Statistical analysis found a negative relationship between total 15N recovery and lignin content after 7 months under greenhouse condition with relatively high of coefficient determination (R2 > 0.5). The APSIM’s SOILN model (version 7.5, was used in this study to predict the kinetics of C and N mineralisation of plant residues from 3 independent dataset. New parameters used for model performance were obtained as following steps: (1) changing FPOOLs size based on measured data from default values as 0.2 : 0.7 : 0.1; (2) allowing the C:N ratios in each FPOOL vary, depending on N content which was determined by optimization; (3) the proportion of the C decomposed from FOM pool that could be retained in the system based on biochemical quality of residues; (4) the proportion of the C decomposed from BIOM and HUM pools retained in the system based on soil characteristics; (5) re-formulation the fraction of retained biomass returned to biomass; (6) re-formulation the fraction of retained FOM transferred to biomass. With these modifications, the model was able to provide reasonable estimates of both C and N release from a wide range of plant residues (C:N ratio varied from 9.1 to 148). Moreover, the available nitrogen content in soil influenced significantly on the performance of the model. For low residues quality, the modified model could not perform well in very poor nutrient in
dc.contributor.coRefereeCorre, Marife Dr.
dc.subject.engPlant residues, C and N mineralisation, SOILN, N recoveryde
dc.affiliation.instituteFakultät für Agrarwissenschaftende
dc.subject.gokfullLand- und Forstwirtschaft (PPN621302791)de

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