| Yield improvement in maize hybrids has been associated with the 'stay green' characteristic (i.e. delayed leaf senescence). Although leaf senescence is a genetically controlled process, it can be manipulated (i.e. accelerated or delayed) by nitrogen (N) supply and the ratio of source (i.e., assimilate supply) and sink (i.e., demand for assimilates) during the grainfilling period. The objective of this research was to establish whether the 'stay green' characteristic in a new maize hybrid is related to an improved source-sink ratio (i.e., ratio between assimilate supply and assimilate demand) and/or a more efficient use of N during reproductive development. A 3-yr field study was conducted with two short-season maize hybrids, Pride 5 (old) and Pioneer 3902 (new), that were grown at two N levels and four source-sink ratio treatments (30% defoliation, control, 50% sink and no sink).;Results of this research confirmed that high dry matter accumulation of Pioneer 3902, relative to Pride 5, was associated with increased leaf area duration, A balanced source-sink ratio was associated with a high number of green leaves, a high crop growth rate, and relatively small remobilization of stover dry matter (i.e., leaves and stem) to the grain, The balanced source-sink ratio was observed for Pioneer 3902 in the control treatment ;Nitrogen uptake after silking was influenced by the source-sink ratio and was higher in Pioneer 3902 than in Pride 5. More than 60% of grain N in Pioneer 3902 and about 40% of grain N in Pride 5 was derived from N uptake during the grainfilling period. Dry matter, soluble carbohydrates, and N content of the lower stem section were influenced substantially by the source-sink ratio and, consequently, were greater in Pioneer 3902 than in Pride 5.;Dry matter and soluble carbohydrate content of the lower stem may indicate assimilate supple to the roots and N accumulation in the lower stem may be an indicator of N uptake during the grainfilling period in maize. |
