Dry Matter Production and Nitrogen Utilization of High Yielding Soybean Cultivars.

Soybean [Glycine max (L.) Merr.] is an important crop for oil and protein. The recent cultivars achieved high yield via greater dry production rather than greater harvest index. The objective of this study is to identify the most important trait related to higher dry matter production. Recent US cultivars and Japanese cultivars were cultivated at a drained paddy field of Takatsuki Experimental Farm, Kyoto University in 2012 and 2013. Irrigation was conducted to maintain optimal soil water condition. Total dry matter of each cultivar was measured at initial seed filling stage (R5) and at maturity (R8). During R5 to R8, abscised leaves and petioles were collected and dry weight was measured. In 2013 nitrogen content, Rubisco content, and SPAD value of the top full expanded leaves were measured periodically after R5. The positive correlation was observed between yield and total dry matter produced after R5 (r=0.374). Rubisco content were maintained in high yielding cultivars after R5. The Rubisco content correlated with nitrogen content, while it did not with SPAD values. These results suggested the high yielding cultivars tend to have higher dry matter production during seed filling period. And higher dry matter production during seed filling was partially explained by the higher Rubisco content. Though still additional measurement of leaf traits related photosynthesis is needed, leaf Rubisco content, rather than leaf nitrogen content, can be a good indicator for selecting high potential biomass productivity during seed fillling.