Effect of Helianthus tuberosus late growth stage of on biological yield and nutritional value

This study aimed to the right time for harvesting Helianthus tuberosus in an area of 667 hm2. According to the different growth periods, the time of harvest was allocated to six sampling points before tuber harvest (i.e., 10, 8, 6, 4, 2, 0 weeks). Based on the topography and soil texture, five different plots were selected for each sampling, and each plot was selected by 1 m2 to allow harvest of the aboveground and underground parts. Plant aboveground parts (lower one-third, middle one-third, and upper 1/3), tuber yields, nutrient components, and gross energy were measured. The results showed that the yield of fresh, air-dried H. tuberosus and its dry matter content in the late growth stages, the yield of different aboveground parts, and underground parts, and whole plants, and the proportion of aboveground and underground changed significantly (P<0.01). The crude protein yield of underground parts was the highest (P<0.01) at the first incidence of frost. The crude protein yield of aboveground parts and whole plant was the highest (P<0.01) at 2 weeks before the first frost. The gross energy yield of aboveground and whole plant was the highest (P<0.01) at 2 weeks before the first frost. However, the yield of underground parts was the highest (P<0.05) at the first frost. The crude protein yield of Helianthus tuberosus was 3 206 kg·ha-1, which was 2% higher than the total protein yield of maize and wheat (3 146 kg·ha-1). The gross energy yield of H. tuberosus was 8.33×105 MJ·ha-1, which was 37% higher than the total protein yield of maize and wheat (6.06×105 MJ·ha-1). Judged from the perspective of feed production, the biological yield of H. tuberosus was the maximum; in addition, the most suitable harvest period for feed was 2 weeks before the first frost. The biological yield of H. tuberosus was better than the total of corn and wheat. H. tuberosus' cultivation is one of the important ways of mitigating bioenergy shortages.