The effect of post-anthesis water supply on grain nitrogen concentration and grain nitrogen yield of winter wheat

The effect of water supply during grain growth on grain nitrogen concentration (GNC) and grain nitrogen yield (GNY) of winter wheat (Triticum aestivum L.) was studied in the field experiment on fertile loamy-clay soil in years 2004–2007. The water regime was differentiated using mobile rain shelter (water shortage, treatment S) and drip irrigation (ample water supply, treatment W); rain-fed crop served as the control treatment (R). Wheat was grown without addition of nitrogen and with 200 kg N/ha (N0 and N1, resp.). The effect of water supply on GNC was highly significant (P < 0.001) in fertilized wheat and not significant in N0. Drought significantly increased GNC in comparison with irrigated and rain-fed crop in N1. Average grain nitrogen concentrations in respective treatments S, R and W were 1.52, 1.54 and 1.56% in N0 and 2.50, 2.24 and 2.07% in N1. Water availability also significantly affected grain nitrogen yield (P < 0.01). The GNY of fertilized wheat under water shortage was significantly lower (139 kg/ha) than GNY in treatments R (174 kg/ha) and W (182 kg/ha) while under N0 the differences were not significant. Unlike GNC, the GNY was positively associated with mineral N supply (Nmin) in 0–90 cm depth in early spring (r = 0.98–0.99 and 0.83–0.97 for N0 and N1, resp.). Several weather and related characteristics showed relations to GNY and GNC, often opposite under N0 and N1. Nmin together with nitrogen fertilization rate, indicators of water regime and temperature during grain growth period explained 78–97% of observed variability of GNC and GNY in the experiment.