2009 Annual Report
1a.Objectives (from AD-416)
Collect data from growers fields, experimental station research plots, and controlled environmental chamber studies. Use these data to refine and improve existing simulation models for corn, soybean, potato, and cotton crops. Evaluate the models under a range of environmental and management conditions.
1b.Approach (from AD-416)
Evaluate the knowledge gaps for CSGCL crop and soil process models and design and conduct controlled environmental studies to develop new data for model development, and validation of the models. The model verifications, validation, and application will be conducted before release of the models to on-farm use by the growers.
Data were collected during the 2008 growing season on corn from a study conducted at Wye Research and Education Center. The experiment evaluated the applicability of SPAD meter in diagnosing corn nitrogen status. SPAD meter readings were collected from the top most leaf as well as the ear leaf. Using the data, a linear relationship between total shoot nitrogen content and top most leaf nitrogen content, and another linear relationship between top leaf nitrogen content and SPAD meter reading were established. These established relationships were also validated using data collected from other locations. The collected nitrogen data were also used to evaluate the performance of MaizSim model in simulating the corn nitrogen dynamics.
The improvements were made to the corn simulation model, MaizSim, in regard to simulating corn nitrogen dynamics include four aspects. First, corn nitrogen demand is described by an allometric function which relates corn nitrogen demand to corn shoot biomass. The determined nitrogen demand is then passed into a soil simulation model, 2DSOIL, for the soil model to simulate active nitrogen uptake by corn; secondly, after nitrogen is taken by a corn plant, it is further partitioned into the leaf and other parts of the shoot. The portion of nitrogen that is partitioned into leaf is simulated as a function of accumulated thermal time after seedling emergence; thirdly, the photosynthesis capacity of corn leaf is directly affected by corn leaf nitrogen content. Finally, in MaizSim, we implemented two kinds of functions that directly link corn leaf nitrogen content to leaf photosynthesis capacity. The first is a linear function. The second is a hyperbola function. In addition, corn leaf expansion is indirectly linked to corn nitrogen status by linking actual leaf expansion rate to actual carbon supply rate, which is related to leaf nitrogen status. The performance of the modified model was evaluated using data collected from year 2007 and 2008. The evaluation results showed that the model simulation of partitioning of nitrogen to corn leaf was reasonable when compared with measured data. The simulation of both leaf expansion and shoot biomass was also improved with the implementations described above. Daily meetings are held to monitor the progress on this project and provide guidance to the post-doc. We also maintain contact with the University of Maryland on a regular basis both by telephone, e-mail, and onsite meetings.