Wheat flag leaf nitrogen content to predict grain protein increase due to topdressed nitrogen at heading

The aim of this work was to determine whether exists a relationship between wheat (Triticum aestivum L.) grain protein content and flag leaf (HB) N concentration at milk stage, and if HB N concentration at heading has predictive value of grain protein content increases due to topdressed N at that stage. Two field studies were conducted in 1995 and 1996 with hard red spring wheat. In 1995 treatments were different preceding crops: corn (Zea mays L.), soybean (Glycine max. (L.) Merr.), and sunflower (Helianthus annuus L.). In 1996 they were tillage systems: conventional (LC) and no-tillage (SD). In both years N fertilizer was applied at preplant (0 and 120 kg N.ha^-1) and topdressed two days after heading (0, 20 and 40 kg N.ha^-1). Topdressed N had no effect on either grain yield or grain weight. Flag leaf N concentrations and grain protein content were both increased by preplant and topdress N applications. For both years, grain protein content was positively correlated with N concentration of flag leaves sampled at milk stage. Topdressed N caused greater increases in grain protein content, when N concentration in the HB at heading was low. It is concluded that, N concentration in the HB at heading is a good indicator of the likelihood of a response in grain protein content to topdressed N at that stage.

Key words: wheat, protein, nitrogen, flag leaf, prediction.