Model of Light Penetration into a Wide‐Row Crop 1

This model predicts direct‐beam radiation penetration into wide‐row crops. The crop is modeled as “hedgerows” with an open middle between the rows. Leaf area density is given height and cross‐row functional distributions, but is considered uniform along the length of the row. Input parameters which can be varied are: time of day, time of year, latitude, longitude, atmospheric trans‐missivity, slope of the soil surface, row direction, row spacing, crop height, width of the hedge‐row, leaf area density distribution functions, and mean leaf angle. The model can predict the average direct‐beam penetration to any depth as a function of distance from the row, and the average penetration for the whole hedge‐row system. Light penetration was predicted for E‐W, N‐S, NE‐SW, and NW‐SE row orientations for August 17, 1967, using row geometry of E‐W wide‐row grain sorghum ( Sorghum bicolor L. Moench) grown at Akron, Colorado. Low predictions of light interception in the morning and afternoon by E‐W rows resulted in the lowest predictions of daily total intercepted light. Under the input conditions, the model predicted 37, 44, 42, and 42% daily interception for E‐W, N‐S, NE‐SW, and NW‐SE row orientations, respectively. The NE‐SW row orientation may be best since the model predicted that the most light would be absorbed at 1000 hours, when moisture stress would be low, and the least at 1400 hours, when moisture stress would be high.