Agricultural chemicals ate a source of groundwater pollution in some areas. Regulatory options to reduce such nonpoint pollution imply costs to producers. By integrating plant simulation, hydrologic, and economic models of farm-level processes, this study evaluates on-fama costs of strategies to reduce nitrate groundwater pollution. The empi¡ focus is on intensively managed, irrigated farms in the Columbia Basin of Oregon. Results suggest that changes in timing and application rates of nitrogen and water reduce nitrate pollution with little loss in profits. Once such practices are adopted, further reductions in nitrates can be achieved only at increasing costs to producers.

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A highly modular structure has been developed for crop growth simulation models and implemented in the SIMPOTATO model, a model based on the standards of the IBSNAT (International Benchmarks Sites Network for Agrotechnology Transfer) project. The model structure features top‐down design, modularity, high cohesiveness, loose coupling, and data hiding. SIMPOTATO is composed of (i) an upper level module to run the model, (ii) an experiment selection module, (iii) an initialization module, (iv) a simulator module, (v) the crop and soil processes module, (vi) a start/stop module, (vii) a report writing module, and (viii) a graphic display module. Each module is composed of one or more subroutines and functions. Such a modular structure facilitates transferring improvements between models, combining models into multi‐crop models and crop/pest models, and modifying models for new applications.

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