Contributions of Pre‐Silking Assimilate to Grain Yield in Maize1

There has been a long‐standing debate among cereal researchers regarding the importance of assimilate remobilization for grain yield. Few estimates have been made of contributions to grain yield of assimilates formed prior to flowering in maize ( Zea mays L.). In field studies on a Waukegan silt loam soil (Typic Hapludoll) at St. Paul, MN in 1982 and 1983, one hybrid (A619 ✕ W64A) was grown under conditions of early and late planting and evaluated for the contribution of pre‐silking assimilates to yield. Individual plants were labelled with 14 CO 2 several times during the pre‐ and post‐silking periods. This treatment was coupled with measurements of changes in aboveground plant dry weight during these same periods. The relative distribution of radioactivity between grain and stover was assessed at maturity. The contribution of pre‐silking assimilates to yield could then be estimated mathematically from the 14 C distribution and dry matter change information. Results showed that most assimilates contributing to grain yield were formed after silking. Less than 10% of the final grain yield for either planting date was attributable to pre‐silking assimilate. Both grain yield and absolute contribution of pre‐silking assimilate to yield tended to be lower in later sown plants. We postulate that most of the 14 C detected in the grain at maturity from labelling dates before silking was translocated with nitrogen remobilized from vegetative organs. Although small quantitatively, these pre‐silking assimilates may be extremely important for optimum development of the grain.