Fig. 3. Mean cereal grain species light transmittance through a winter cereal grain canopy to the top of a red clover intercrop canopy grown near Ames, IA. Means are averaged across cereal grain seeding rates of 100, 200, 300, and 400 seeds m^–2. GDD = {[(daily max. temp. + daily min. temp.)/2] – base temp.} > 0 with base temperature = 0°C.