Winter wheat and cheat seed response to foliar nitrogen applications

Abstract

Growing winter wheat (Triticum aestivum L.) cultivars in a weed‐free environment is necessary for optimum grain yield. Cheat (Bromus secalinus L.) is an important grass weed in winter wheat and can cause grain yield loss in excess of 40% in heavily infested fields. Two field experiments were conducted during the 1994–95 and 1995–96 crop years to evaluate the effect of foliar nitrogen (N) fertilizer on wheat grain yield and quality, and cheat seed reduction in winter wheat. Foliar fertilizer solutions were urea ammonium nitrate (UAN), ammonium hydroxide (NH₄OH), and ammonium sulfate [(NH₄)₂SO₄]. Wheat varieties were ‘Tonkawa’, ‘Longhorn’, and ‘Jagger’. Foliar N was applied after winter wheat had completed flowering, but one to two wk prior to cheat flowering in an attempt to desiccate immature cheat heads. Wheat grain yield, grain protein, and cheat seed yield were determined after harvest. Wheat grain yield was not affected by foliar applied N following wheat flowering, while wheat grain protein increased 1 to 4%. Foliar N applications significantly reduced cheat seed production. Linear‐plateau models indicated that cheat seed reduction (percent germination * cheat yield versus check) ranged from 41.7 to 70.3% when foliar N was applied at rates between 0.4 and 19.4 lb N acre⁻¹ prior to cheat flowering. Average cheat seed reduction over years, N source, and variety was 54.9% when N was foliar applied at an average rate of 6.7 lb N acre⁻¹. This reduction in the cheat population could prove to be beneficial to subsequent winter wheat crops. Similar differences in flowering between weed and crop in other production systems may reveal additional windows of opportunity for applying foliar N fertilizers aimed specifically at weed control.