Abstract: Chinese milk vetch (CMV) is widely used as a winter green manure crop in China. CMV has a long flowering period and an indeterminate flowering habit, meaning that pods at basal nodes mature first and pods at higher nodes mature later. This research was conducted in Xinyang, Henan provinces, and studied how seed yield traits change with pod maturity status at different node positions of plants and at different times after the full-bloom stage of crop development, in order to develop harvest regimes to optimize seed yield. It was found that pod biomass increased as pods matured and that pod biomass of the 1st-2nd node sites was higher than that of the 5th-6⁺th node sites. The total seed yield increased with days from full bloom (yield at 26 d≈33 d>19 d>12 d>5 d), and the maximum yield was 123.2 g·m^-2 at 33 days after full-bloom growth stage. The seeds from the 1st-4th node sites accounted for more than 80% of the total seed yield. Pod ripening was stratified and occurred in a progression from lower nodes to upper nodes. Pod maturity was measured using a Ⅰ-Ⅵ scale and the maturity index of pods on the 1st-4th node sites showed a sigmoid curve over time, while the maturity index of pods on the 5th-6⁺th node sites displayed an exponential shape. Rapid ripening occurred at 12-26 d after full-bloom for pods on the 1st-4th node sites, and at 19-33 days after full-bloom for pods on the 5th-6⁺th node sites. As maturity status progressed from Ⅰ to Ⅵ, the pod color changed from light-green to deep-black, and the pod length and width of the largest pod within each inflorescence increased up to four-fold and two-fold, respectively, while the 1000-seed weight increased six-fold. The rate of change of seed yield relative to maturity index for pods on the 1st-3rd node sites was 2.58 times that of pods on the 4th-6⁺th node sites. On the basis of the maturation patterns and seed yields observed, it is clear that the lower and middle pods should be the key focus of seed production of CMV. The time when the uppermost pods reached maturity state IV was found to be a convenient indicator of maximum crop seed yield.

Key words: Astragalus sinicus, stratified maturation, pod traits, seed yield