S25 - Session P1 - Effect of nitrogen rate on the nitrogen uptake and root yield of Achyranthes bidentata

Authors: Stephen Harper *, Binh Nguyen, Hien Phan Thuy, Dang Ha, Chu My, Duyen Nguyen, Phuong Pham

The extract from the roots of Achyranthes bidentata (Blume) has long been used in Vietnam and other Asian countries as a valuable medicinal material. Although production areas have increased, maximising root yield is also required to meet demand. The aim of this study was to identify the effect of nitrogen (N) on N-uptake and yield of A.bidentata . A field experiment was conducted on sandy loam soil (0.15% N total) at Thanh Tri (Hanoi, Vietnam) with nine rates of nitrogen (0, 35, 70, 105, 130, 155, 180, 205 and 260 kg ha -1 ) as urea. Urea was dissolved and applied in 5 splits at 0 (10%), 20 (20%), 40 (25%), 60 (25%) and 80 (20%) days after sowing. Seeds were sown directly in October 2016 with 5 replicates in a randomised complete block design and harvested 130 days after sowing. The root dry matter yield increased (from 2.9 to 3.3 t ha -1 ) when N increased from 0 to 70 kg N ha -1 . Root dry yield decreased gradually (to ~2.1 t ha -1 ) when the N-rate application was further increased up to 260 kg ha -1 . Foliage dry matter yield increased from 2.9 to 4.0 t ha -1 with N rates increasing from 0 to 205 kg ha -1 , but application of 260 kg ha -1 N caused a reduction in the foliage dry yield (3.7 t ha -1 ). The N-rate was positively correlated with N content in roots (r=0.87) and foliage (r=0.72). The N-uptake was highest (206 kg ha -1 ) at the N-rate of 205 kg N ha -1 and lowest (~77 kg ha -1 ) at the rate of 0 kg N ha -1 . In conclusion, application of 70 kg N ha -1 gave the best root yield of A. bidentata on this soil. Higher N-rates increased foliage yield but depressed root yield.