A careful study of the output of simulation models can help students understand concepts of crop production and soil management. Very often, graphical representation of the simulated data allows faster and easier understanding of the different processes occurring in a particular system. N-Show is an educational computer program that produces a dynamic, graphical representation of results generated by CERES--Maize, a simulation,model of corn (Zea mays L.) growth and development. The program allows the user to observe and compare the results of several runs of CERES--Maize, which were selected to demonstrate the effect of soil type and N rate on nitrate leaching. N-Show displays dynamic graphs of water and inorganic N contents in the soil, N in the plant, and N leached out of the soil profile. The unique feature of N-Show is that it allows the user to move the graphical display back and forth in time, thereby allowing careful study of the events that occur at specific times. N-Show could be used in undergraduate crop and soil courses and in training sessions for extension workers and farmers. CROP be useful tools for SIMULATION MODELS can teaching concepts related to crop production and soil management (Holt et al., 1976; Waldren, 1982; Meisner et al., 1991). Studying changes in specific variables (i.e., soil inorganic N, crop N uptake, etc.) with time can help students understand the underlying processes in a particular system. Very often, graphical representation of the data allows faster and easier understanding of existing relationships between variables. Two of the possibilities for graphically representing changes in several variables with time are: (i) to display the instantaneous value of each variable (for example in a vertical bar graph with a bar for each variable) and continuously update those values as time proceeds, and (ii) to display the value of each variable in the y axis and time in the x axis (a separate line for each variable). The fist option has the advantage of allowing the display of more variables, because no space is used for displaying the time dimension. Thus, the first option is attractive when the display space is limited, as is the case with typical computer monitors. Models that continuously update the display of variables usually provide a dynamic graph that changes as time moves forward (i.e., SWIM model from Ross, 1990; Scientific Software Group, 1993), but do not allow users to move the display forward and backward in time at their own will. In many cases, it would be convenient to move the display back and forth in time so that relationships between different variables can be better analyzed and Dep. of Crop and Soil Sciences/Institute of Ecology, Plant Sciences Bldg. 3401, Univ. of Georgia, Athens, GA 30602. Received 8 July 1993. *Corresponding author (mcabrera@uga.cc.uga.edu). Published in J. Nat. Resour. Life Sci. Educ. 23:43-45 0994). understood. N-Show is a computer program that provides students with that capability when analyzing simulated results related to the fate of N in soils. The program generates a dynamic, graphical representation of simulated results obtained with the CERES--Maize model (Jones-and Kiniry, 1986). MATERIALS AND METHODS Because the main objective of developing N-Show was to help students understand aspects of N cycling in a cropping systems, I chose the CERES--Maize model to generate the simulated results to be displayed. Soil files were prepared for two soils, a Cecil loamy sand (clayey, kaolinitic, thermic Typic Kanhapludults), representative of the Georgia Piedmont region, and a Tifton sandy loam (fineloamy, siliceous, thermic Plinthic Kandiudults), representative of the Georgia Coastal Plain region. Soil properties for 1.8-m profiles were provided in 10-cm increments for the upper 30 cm, and in 30-cm increments for the rest of the profile (Table 1). For each soil, simulation runs were made with N rates of 100, 200, and 300 kg N ha -l. The N applications were split in three equal amounts applied at planting, and at 41 and 62 d after planting. CERES--Maize version 2.1 was modified slightly to save (in one of the output files) some data that are normally generated by the model but are not saved to file. The modified output file provided values of soil nitrate concentrations in each layer, plant-extractable water content, total N uptake by corn, and total N leached below 1.8 m. These values, recorded every 7 d, are used by N-Show to provide a dynamic representation of the data.