Is There a Role for Sink Size in Understanding Maize Population–Yield Relationships?

The most consistent change in management practices associated with the increase in maize ( Zea mays L.) yield in the United States since 1930 has been a steady increase in plant population. Populations increased from roughly 30,000 plants ha –1 at the beginning of the hybrid era to >75,000 plants ha –1 in recent years. The purpose of this review was to evaluate the potential role of sink size in historic maize yield–population relationships. The steady increase in yield (∼4×) during the hybrid era required an increase in source activity since there was no change in harvest index. The increase in grain yield was associated with an increase in kernels per unit area, so there was a concomitant increase in both source and sink. Data collected from the literature and evaluations of hybrids from different eras demonstrate that ear size (kernels per ear) of U.S. and Canadian hybrids did not increase during the hybrid era. Ears per plant did not increase above an average of one. Since ear size and prolificacy did not change, higher plant populations were needed to increase sink size (ears and kernels per unit area). This approach to analyzing population–yield relationships suggests that higher populations didn't necessarily contribute directly to higher productivity; rather, the increase in sink size avoided a sink limitation and allowed the higher productivity of the source to be translated into grain yield. Future yield increases will, therefore, require even higher populations which could create new management challenges.