Modeling light availability for a subordinate crop within a strip-intercropping system

The shift of rural laborers out of the agricultural sector led to a steady decrease of intercropping in the North China Plain (NCP). Strip intercropping facilitates mechanized management, and has the potential to out yield monocropping by an optimized resource use of the intercropped species. Therefore we developed a light partitioning model, that calculates the available amount of photosynthetically active radiation (PAR) at the top of the canopy for a given point within a strip of a smaller, subordinate crop. The model was described, evaluated on various simulation time steps and tested for the purpose of designing strip-intercropping systems. PAR reaching the top of the canopy of various rows of the strip subordinate bush bean (Phaseolus vulgaris L var. nana) was measured continuously under different sky conditions. In the dominant strip, maize (Zea mays L) was grown. Then the model was tested for its ability to account for the influence of different widths of the bush bean strip, strip orientations and maize canopy architecture (height, leaf area index, and leaf angle distributions). Comparison between hourly averaged simulated and observed values of PAR across the bush bean strip showed a high accuracy of the simulations, under both, clear and cloudy conditions. Overall, simulations of hourly values of PAR across the bean strip showed a root mean square error (RMSE) ranging between 47 and 87 p,mol m(-2) s(-1) and a percent bias (PBIAS) ranging between -3.4 and 10.0%. A simulation time step of 20 min is recommended to preserve the accuracy of the model across the strip. The model captured reasonably the influence of strip design (width and orientation) and maize canopy architecture. Results suggested that the highest potential to increase PAR across the bush bean strip is by reducing height and leaf area index of maize, especially in the most shaded border row adjacent to the maize strip. The model proved to be a helpful tool for understanding the characteristics of light availability across the strip of the subordinate species and can be further used to examine a number of strip intercropping arrangements prior to labor and time consuming field trials. (C) 2013 Elsevier B.V. All rights reserved.