Study on the relationships between the accumulation and translocation of dry matter and nitrogen and flower/pod development into seeds and seed yields in Chinese milk vetch.

Further improvements to the yield potential of Chinese milk vetch seed are essential for the planting demand of green manure. Flower and pod development directly determines the number of seeds and the seed yield of Chinese milk vetch. However, the accumulation and translocation of dry matter and nitrogen between plant organs directly affects flower and pod development and morphological formation. There are few studies that analyse the relationship between the accumulation and transport of dry matter and nitrogen and the number of flowers, pods, grains and seed yield during Chinese milk vetch's critical development period. This study aimed to determine the seed yield response to dry matter and nitrogen accumulation and translocation during the Chinese milk vetch growth period and to quantify the relationship between these factors to predict Chinese milk vetch seed yield. Experiments were performed during the 2017-2018 and 2018-2019 growing seasons at the Dayuzhuang experimental field. The first experiment involved five foliar application stages (late wintering stage, returning green stage, squaring stage, pre-flowering stage, and 5 days after flowering) and six foliar application concentrations of borate solution (0, 500, 1000, 2000, 4000, and 6000 mg L-1). Experiment 2 included five foliar application stages (late wintering stage, returning green stage, squaring stage, pre-flowering stage, and 5 days after flowering) and six foliar application concentrations of paclobutrazol (0, 200, 300, 400, 500, and 600 mg L-1). When the dry matter mass in the full flowering stage was 3500-4500 kg hm-2, the seed yield reached more than 800 kg hm-2. When the translocated assimilates were stored in the vegetative organs before flowering, the assimilate translocation rate and their contributions to seed yield were 1500-1800 kg hm-2, 30-35%, and 28-38%, respectively, and the Chinese milk vetch seed yield was predicted to reach 800-1000 kg hm-2 at maturity. When the nitrogen translocation amount in the vegetative organs before flowering, the nitrogen translocation rate, and the contribution rate to the seed yield were 68-78 kg hm-2, 65-75%, and 75-85%, respectively, the Chinese milk vetch seed yield was predicted to reach 800-1000 kg hm-2 at maturity. If the accumulation and translocation index values of dry matter and nitrogen were lower or higher than the above ranges, the seed yield was lower than 800 kg hm-2. The results of this study revealed the mechanism by which dry matter and nitrogen accumulation and translocation affect the Chinese milk vetch seed yield. These findings enrich the seed yield formation theory of Chinese milk vetch. They provide an early determination and quantitative regulation of high and stable seed yield for Chinese milk vetch in the field and aid researchers to integrate multiple production technologies for the sustainable production of Chinese milk vetch.