Effects of nitrogen application level on physiological indexes and agronomic properties for cassava

In order to improve the using efficiency of N fertilizer，a field experiment was conducted to investigate the effects of nitrogen application（0，65，130，195 kg N/hm2）on the physiology，yield and quality of cassava cultivar Xinxuan056. Results showed the peroxidase activity，catalase activity，proline content，chlorophyll content and soluble sugar content in leaves increased obviously at both root expanding and root mature stages，as the nitrogen increased from 0 kg/hm2 to 130 kg/hm2，but malondialdehyde content in leaves decreased obviously. The physiological properties of leaves changed slightly when the amount of nitrogen application was higher than 130 kg/hm2. The plant height，fresh root yield，fresh root starch content and fresh root starch yield increased by 7.43%-24.36%， 5.77%-11.55%，3.96%-10.73% and 9.96%-24.12% respectively after nitrogen applieation，and their increments increased with the increment of nitrogen applied，but the yield traits and quality traits were not significantly different between 130 kg N/hm2 treatment and 195 kg N/hm2 treatment. Therefore，the optimum level of nitrogen fertilizer for cassava was 130 kg/hm2.