Response of hedysari radix nitrogen absorption and polysaccharide accumulation to fertilizer application

It is critical to establish a standard cultivation procedure for hedysari radix, and explore new ways of using less fertilizer for high yields of Chinese herbal crops, and provide theoretical basis for the application of palygorskite in cultivating Chinese traditional medicine. To that end, a field experiment was conducted to study the dynamics, absorption and distribution of nitrogen and polysaccharides in hedysari radix. The effects of palygorskite application rates of 750 kg·hm^-2 (P1), 1 500 kg·hm^-2 (P2) and 2 250 kg·hm^-2 (P3) with NPK fertilizer on nitrogen absorption and polysaccharide accumulation in hedysari radix were also analyzed. The results showed that the critical period of nitrogen nutrition in aboveground part of hedysari radix was late June to late July. However, increased nitrogen requirement by the root system of hedysari radix was noted in late August. From late September to late October, nitrogen transfer occurred from aboveground part to belowground tissues. Also from late June to late August, the content of polysaccharides sharply increased in the root system of hedysari radix plant. Compared with only NPK application, combined application of palygorskite and NPK fertilizer increased N content at the late growth stage of the plant. It also increased N content in roots and active aboveground growth tissues. Compared with NPK treatment, NPK+P3, NPK+P2 and NPK+P1 treatments increased hedysari radix N accumulation at harvest by 45.22%, 29.45% and 20.06%, respectively. N accumulation in the aboveground part of the plant under NPK+P3 treatment increased by 71.99%, compared with NPK treatment. N accumulation in the root system under NPK+P3 and NPK+P2 treatments increased by 38.72% and 26.07%, respectively. NPK+P3 treatment promoted N accumulation and prolonged the period of N accumulation in the aboveground part of hedysari radix at the early growth stage. It also delayed N de-accumulation in the aboveground part of the plant at the late growth stage. NPK+P3 and NPK+P2 treatments enhanced the rate of N accumulation in roots. They also increased single plant root N accumulation over NPK treatment. The content of polysaccharides under NPK+P1, NPK+P2 and NPK+P3 treatments increased by 50.74%, 62.95% and 40.63%, respectively, over NPK treatment. The combined application of palygorskite and NPK prolonged accumulation time of polysaccharides in hedysari radix. While it delayed polysaccharide de-accumulation in roots, and improved overall polysaccharide yield of the plant. The comprehensive performance of N absorbing capacity under combined application of palygorskite and NPK was in the following order: NPK+P1 (high rate) > NPK+P2 (medium rate) > NPK+P3 (low rate). The further studies on this observed correlation between palygorskite and polysaccharide output were recommended.