THE EFFECT OF N PLACEMENT ON GRASS WEEDS AND WINTER-WHEAT RESPONSES IN 3 TILLAGE SYSTEMS

Field studies were conducted for three seasons (1978-1979, 1979-1980 and 1981-1982) on a Palouse silt loam near Pullman, Washington, to compare the effects of broadcast and deep banding of nitrogen (N) fertilizer beneath winter wheat (Triticum aestivum L.) seed on N uptake and dry matter production of downy brome (Bromus tectorum L.) and jointed goatgrass (Aegilops cylindrica Host.), and on N uptake, dry matter production and grain yields of winter wheat. Three tillage systems were used: conventional tillage; shallow roto-tilling, or no-tillage prior to planting. Rates of N were 0, 65, 130 and 190 kg N ha-1 as ammonium nitrate. Additional plots were maintained free of weeds at the 130 kg N ha-1 rate. In 1983-1984, deep banding of the fertilizer between rows in a paired-row configuration was compared to surface-broadcast N fertilizer using N rates of 0, 45, 90 and 135 kg N ha-1. There were no significant differences between broadcast and deep-band application of N on grass weed N uptake or dry matter production with mold-board plowed or no-tillage, but there was greater weed growth with surface-broadcast N with shallow roto-tilling. Wheat N uptake, growth and grain yields were consistently higher with band-applied N compared to broadcast N. The yield response to banding N was the same with or without the presence of grass weeds. © 1990.