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Modelling crop growth and biomass partitioning to shoots and roots in relation to nitrogen and water availability, using a maximization principle. II. Simulation of crop nitrogen balance |
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| Authors: | Jouko Kleemola Matti Teittinen Tuomo Karvonen |
| Institution: | a Department of Plant Production, PO Box 27 (Viikki), FIN-00014 University of Helsinki Helsinki Finland b Laboratory of Hydrology and Water Resources Engineering, Helsinki University of Technology, Konemiehentie 2 FIN-02150 Espoo Finland |
| Abstract: | This study analysed of the ability of a crop model to simulate crop nitrogen (N) balance. The model was originally developed to serve as a foundation to develop a decision-making tool to analyse the impact of water management and nitrogen fertilization on crop yield. The model included a dynamic parameter for allocation of dry matter between root and shoot allowing root to shoot ratio to vary according to differing environmental conditions. The new allocation parameter was introduced in order to make the model more applicable under water and nitrogen limited growing conditions. Two wheat (Triticum aestivum L.) data sets were used to test the model simulations. Generally, the model simulations agreed well with the recorded data on crop N uptake. The relationship between the actual and simulated amount of N taken up by the crop was close in the calibration treatments of a greenhouse experiment. The coefficient of determination (r2) of the regression line (simulated value = independent variable, measured value = dependent variable) was 0.90. The r2 was 0.83 for the validation data. In the field experiments, the r2 values were 0.91 for the calibration data and 0.82 for the validation data. In field data, the model underestimated in some cases the crop N uptake during the period when actual shoot dry weight increased exponentially in spring. Therefore, methods used in computation of nitrogen uptake have to be analysed further. Plant organ N content was simulated satisfactorily for both greenhouse and field data. However, the range over which the simulated values varied was larger than in the actual data. The results from the study indicate that our model is capable of simulating the crop N balance and we suggest that the model could be used when developing an N application decision tool for field crops. However, the availability of N and soil water were provided as inputs in the present study. Thus, the model should be integrated with models simulating below ground processes in the future. Moreover, the model should be further validated with actual field data. |
| Keywords: | Crop modelling Nitrogen relations Nitrogen uptake Spring wheat Triticum aestivum L Water relations |
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