ChileanJAR

Two experiments were conducted, through additive design, to evaluate the effect of increasing densities of wild oats (Avena fatua) and Italian ryegrass (Lolium multiflorum), separately, on winter and spring production of wheat (Triticum aestivum L.) at two locations in Chile. Wild oat densities between 0 to 16 plants m^-2 in the Andean foothills, and 0 to 24 plants m^-2 in the irrigated valley, and Italian ryegrass densities between 0 to 50 plants m^-2 in the Andean foothills, and 0 to 80 plants m^-2 the irrigated valley were used. A hyperbolic model was fitted to the data to predict wheat yield and loss. Every additional wild oat plant m^-2 reduced wheat yield by approximately 100 kg ha^-1, while every additional 10 Italian ryegrass plants m^-2 reduced wheat yield about 140 to 200 kg ha^-1. Wild oat densities of 3 plants m^-2 reduced wheat yield by 4.5% in the irrigated valley, and 3.5% in the Andean foothills, respectively. Italian ryegrass densities of 10 plants m^-2 reduced wheat yield by 1.6% at the irrigated valley and by 1.3% at Andean foothills, respectively. With the losses projected by the hyperbolic model, the economic threshold varied between 3 and 4.4 wild oat plants m^-2, and 27 and 36 Italian ryegrass plants m^-2 depending on the agroecological area and weed control cost. There was a linear relationship between the number of uncontrolled weeds and the density of weed seeds in the wheat. The largest wild oat density of 24 plants m^-2 increased the soil seed bank by 2,000 seeds m^-2, while the largest Italian ryegrass density of 80 plants m^-2 increased the soil seed bank by more than 28,000 seeds m^-2.