Effects of topdressing nitrogen on apparent quality, dry matter accumulation and contents of active components in the root of Isatis indigotica Fort.

Effects of topdressing nitrogen on the photosynthetic parameters of Isatis indigotica Fort., apparent quality, dry matter and active components of the root of Isatis indigotica Fort. was studied to explore the physiological effects of nitrogen fertilizer on the growth of shoots and roots, and to find the best preferred nitrogen fertilizer application rate. A field experiment was carried out using five processing nitrogen treatments with three repeats, and the amounts of nitrogen fertilizer were 225 kg/ha, 450 kg/ha, 675 kg/ha, 900 kg/ha and 1125 kg/ha, respectively. The results show that the nitrogen fertilization has a strong root effect by improving the photosynthetic parameters（Pn, Gs, Ci and Tr）, and significantly increases the main root diameter and root length. The total fresh weight increased with nitrogen rate, but no longer increasing with more than 900 kg/ha. The number of lateral roots was the least under 450 kg/ha. The numbers of lateral roots were increased significantly under the low nitrogen (225 kg/ha) and the high nitrogen (900 kg/ha and 1125 kg/ha), which affected the medicinal appearance quality of the root of Isatis indigotica Fort.. With the increase of nitrogen rate, the dry matter accumulation amounts of leaves and roots were increased firstly, and then decreased, and the dry matter of leaves and dry matter of roots were maximum under the 900 kg/ha and 675 kg/ha, respectively. But the root-shoot ratio was declined with the increase of nitrogen rate. It indicates that the promotion effect of topdressing nitrogen fertilization on the leaves is larger than that of the roots. With the increase of nitrogen rate, the polysaccharide content was increased firstly, and then decreased, and the content of polysaccharide was the maximum (158.383 mg/g) under the 675 kg/ha. The variation of the content of (R,S)-epigoitrin was not very clear, which was the maximum (0.5655 mg/g) under the 900 kg/ha. The suitable nitrogen application amount was 675 kg/ha - 900 kg/ha to ensure production and medicinal quality of the root of Isatis indigotica Fort..