Growth of Bean Strip-Intercropped with Maize: Evaluation of the CROPGRO Model

Optimizing strip-intercropping systems requires a comprehensive modeling approach to study competition effects, especially for solar radiation, and to integrate numerous crops. Therefore, we studied the radiation availability and its effect on canopy and leaf level and finally on total dry matter and yield formation of bush bean (Phaseolus vulgaris L. var. nana) strip-intercropped with maize. Nine rows of bush bean were sown on two sowing dates between strips of six rows of maize (Zea mays L.). The CROPGRO model was tested with an hourly input of solar radiation for its ability to simulate observed growth and yield formation of the two most shaded bush bean rows next to maize. Experimental results showed that bush bean had a good potential for strip-intercropping systems tolerating up to 30% shading due to an increased light interception by a larger canopy with a considerable increase in its leaf area. The CROPGRO model, calibrated on data of monocropped bush bean, captured well the effect of the strongly reduced radiation on total and pod dry matter in the most shaded bush bean row. This indicates the model's applicability on other intercropping systems exhibiting high levels of shading. Under a lower level of shading further from maize, cultivar parameters responsible for leaf area expansion and the maximum photosynthetic rate had to be increased to achieve a high accuracy of the simulations. Future studies should focus on measurements of photosynthesis, radiation distribution and absorption within the canopy, and leaf area expansion under shaded conditions to improve model simulations.