Vertical distribution of nitrogen in different layers of leaf and stem and their relationship with grain quality of winter wheat

With the widespread application of remote sensing (RS) in agriculture, monitoring and prediction of crop quality attracts the attention of many scientists. Because different vertical layers of crop canopy make different contributions to the spectral reflectance, it is important to define the contributions of different layers to spectral reflectance in order to improve the accuracy of canopy information retrieval using RS data. In this study, vertical distribution of nitrogen in the canopy of winter wheat (Triticum aestivum L.) of two cultivars treated with four nitrogen (N) rates (0, 150, 300, and 450 kg N.hm(-2)) and its contribution to grain quality were investigated. The two cultivars, Jingdong8 (low grain-protein content) and Zhongyou9507 (high grain-protein content), were contrastive in grain quality. Wheat canopy was cut into 3 (at elongation) or 4 (at anthesis and grain filling) layers of equal vertical thickness from top to bottom (layer 1 represented the top, layer 3 or 4 the bottom) in a 1 m2 investigated area of each plot. The objectives of this study were (1) to clarify the N condition of different layers at different growth stages and at various N treatments; (2) to analyze the relationship between N in different layers and grain quality, as well as investigate the contribution of different canopy layers to grain quality; and (3) to provide new data on wheat quality factors in combination with N of different canopy layers potentially to aid retrieval of wheat quality by RS data. The results showed that leaf N concentration decreased from top to bottom. A greater vertical N gradient was observed in leaf than in stem. Leaf N in layer 1 and layer 2 contributed significantly to the grain protein content (GPC) and wet gluten content (WGC) in Jingdong8. Grain quality parameters were significantly related to leaf N in layer 1 of Zhongyou9507. Stem N in Zhongyou9507 made a greater contribution to grain quality than that of Jingdong8. N translocation form the lower layers to the upper layers was associated with grain quality, especially in Zhongyou9507. Greater leaf N gradient 2 (G2) of Zhongyou9507 at anthesis and grain filling was associated with better grain quality.