Effect of barley plant density on wild oat interference, shoot biomass and seed yield under zero tillage

Abstract

There has been little research aimed at developing regression models to describe the effects of barley and wild oat plant density on barley yield loss, or wild oat biomass and seed yield. Such models are an important component of integrated weed management systems, and can help determine when weed control with herbicides is economical. Field experiments were conducted over 4 yr at Vegreville, Alberta, to determine the interactive effects of wild oat and barley plant density on barley and wild oat variables in a zero tillage system. A nonlinear regression model in most cases provided good descriptions of barley yield loss, wild oat shoot dry weight, and wild oat seed yield as functions of wild oat and barley plant densities. The interactive effect of wild oat and barley plant density on percentage barley yield loss did not differ significantly (P = 0.05) among years. A pooled regression model describing barley yield loss accounted for 57% of the variation, and provides a means of estimating yield loss due to wild oat in barley grown under zero tillage. Barley yield loss increased as wild oat density increased but the magnitude of the yield loss diminished with increasing barley plant density. Wild oat economic threshold densities varied among years, and were strongly influenced by barley price and expected wild oat-free yield. Economic thresholds were greater at higher barley plant densities. Barley seed weight decreased with increasing barley plant density, and to a lesser extent with increasing wild oat density. The interactive effect of wild oat and barley plant density on wild oat seed yield varied significantly with year, and appeared to be influenced by climatic conditions. The cooler, wetter spring of 1996 favored wild oat seed production (by several orders of magnitude) compared with the relatively warmer and drier spring of 1995. Each year wild oat seed yield and shoot dry weight decreased as barley plant density increased. The results suggest that seeding barley at relatively high rates may reduce the need for wild oat control with herbicides in zero tillage systems. Key words: Zero tillage, wild oat interference, barley seeding rate, nonlinear regression