Modeling biomass growth, N-uptake and phenological development of potato crop

Using the modeling tool Expert-N, daily fluxes of water, carbon and nitrogen in potato fields were simulated in this study. The crop growth model Soil-Plant-Atmosphere System Simulation (SPASS) was integrated in Expert-N and adapted for the simulation of potato growth. The aim of the study was to investigate the extent to which the SPASS model, tested thus far only for winter wheat, is suitable for the simulation of potato crops. In addition to re-parameterization of the model, minor modifications, such as description of phenological development, assimilate partitioning, nitrogen uptake and leaf senescence were carried out without changing the overall structure of the model. The SPASS model was calibrated using data from a potato field experiment carried out in 1996 at the Research Station Scheyeru, which examined the effects of various fertilization applications on the growth and yield of two potato varieties, "Christa" and "Agria", representing early and late maturity classes, respectively. Distinctions between "Christa" and "Agria" were realized by variable parameter values concerning phenological development, assimilate partitioning and nitrogen concentration in tubers. The model's ability to predict potato yields and nitrogen uptake was compared with actual values obtained in different years at other fields of the Research Station (only "Agria"). Simulation results show that the SPASS model was able to describe the effect of different N fertilizer applications on potato growth and nitrogen uptake. Differences between the two potato varieties could be adequately predicted, and tuber yields and nitrogen uptake well predicted. However, estimated modeling efficiencies suggest that further improvements are due. Crucial components of the model are the control of root nitrogen uptake and the regulation of the distribution of assimilates to different plant organs. To obtain a broader basis for the verification of the corresponding simulation modules, further experiments addressing optimal nitrogen concentrations in plant organs are necessary. Efforts to refine the SPASS model should be concentrated on a dynamical description of the partitioning pattern of assimilates, including a direct response of the partitioning pattern to changing environmental conditions.