EFFECT OF LIGHT ON WINTER-WHEAT (TRITICUM-AESTIVUM) AND ITALIAN RYEGRASS (LOLIUM-MULTIFLORUM) COMPETITION

Laboratory and field experiments were conducted to determine whether m anipulation of radiation environment during the period of winter wheat establishment can be used to improve wheat yields in Italian ryegrass -infested fields. Percentage of total irradiation and ratio of red (R) light (around 660 etam) to far-red (FR) light (around 730 etam) reach ing the soil surface were important factors in regulating Italian ryeg rass germination, growth, and competitive interactions with wheat. Red ucing total irradiation to about 10% of full sunlight while maintainin g the normal R/FR ratio of about 1.0 reduced wheat grain production in the presence of Italian ryegrass by about 40% compared with weed-free wheat in full sunlight. Further, reducing total irradiation to 3% of full sunlight plus reducing the R/FR ratio to about 0.2 reduced wheat grain production competing with Italian ryegrass by about 35% compared with production in the control conditions. Wheat production of dry ma tter, spikes, and seeds in the presence of Italian ryegrass increased more than threefold under both shading treatments compared with produc tion in full sunlight.