MECHANISTIC PROCESS-LEVEL CROP SIMULATION MODELS FOR RESEARCH AND ON-FARM DECISION SUPPORT
Title: Simulation of nitrogen demand and uptake in potato using a carbon-assimilation approach
Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: April 5, 2008
Publication Date: August 1, 2008
Citation: Timlin, D.J., Kouznetsov, M., Fleisher, D.H., Kim, S., Reddy, V. 2008. Simulation of nitrogen demand and uptake in potato using a carbon-assimilation approach. In: Ma, L., Ahuja, L.R., and Bruulsema T., editors. Quantifying Understanding Plant Nitrogen Uptake for Systems Modeling. Boca Raton, FL: CRC Press. p. 219-243.
Interpretive Summary: Nitrogen is an important nutrient for crops and large amounts are added to soil as an amendment. The amount of fertilizer nitrogen taken up by plants is proportional to their growth rate. If plant growth is reduced by environmental factors, excess nitrogen not taken up by the crop may become a potential pollutant in ground-water. Computer simulation models of crop growth can be useful tools to help farmers, farm managers, consultants, and agricultural researchers to match nitrogen application rates with crop need. The research results were used to develop a new approach to simulating nitrogen uptake in plants. The results of this research will result in more robust models of crop growth that can be used for assessment and management of nitrogen use by plants as related to their rate of growth and environmental conditions.
An understanding of how plants regulate and take up N is important if models are to simulate N dynamics realistically. Many current models consider critical percentages of N in plants in order to calculate demand and account for the effects of N availability on plant growth. Our objective was to quantify the relative amounts of active and passive N (as nitrate) uptake, and carbon assimilation rates in potato under a range of six soil N contents (2, 4, 6, 8, 11, and 14 mM N) and two CO2 levels (370 and 700 umol M-1). A second objective was to evaluate an approach to simulate active and passive N uptake using the soil model 2DSOIL and a simple crop model to determine how well the overall approach describes measured phenomenon. In the model, nitrogen uptake is regulated by carbon assimilation rate, concentration of nitrogen in the soil, and two parameters of the Michaelis-Menton equation, maximum N flux rate and the concentration of N in the soil where the flux rate is one half the maximum. The experiments were carried out using pots in daylit growth chambers with temperature and CO2 control. The crop was potato (Solanum tuberosum L.). Carbon assimilation and transpiration rates, light interception, and end of season biomass and N contents were measured. Total N uptake was calculated from carbon assimilation rates and N contents, N uptake by mass flow was calculated from transpiration and soil N content and diffusive fluxes were calculated by difference. Mass flow rates of N uptake were less than diffusive rates and the difference increased with decreasing N application rate. Simulated trends were similar to measured. The results indicated that simulation of N uptake using carbon assimilation, C/N ratio, and soil N content to regulate N uptake is a useful approach.