Relationship between Assimilate Source and Reproductive Sink in Maize Grown in a Short‐Season Environment1

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Abstract
Limitations to grain yield in maize (Zea mays L.) not explained by unfavorable factors such as disease, nutrient deficiency, or moisture stress may be analyzed in terms of assimilate supply to the grain (the source) and the potential of the grain to accommodate assimilate (the sink). In order to determine whether sink or source represented the first limitation to grain yield, an early‐maturing maize hybrid was grown in field tests at the Elora Research Station near Guelph, Ontario, Canada, during 1973, 1974, and 1975. Sink strength was manipulated by means of light enrichment or shading treatments applied from 2 weeks before until 2 weeks after mid silking. Light‐enrichment and shading treatments applied during the grain‐filling period (i.e., from 2 weeks after mid‐silking to maturity) served to provide information as to whether source capability during grain filling was a dominant limitation to grain yield. Grain yield was affected more by alterations in assimilate supply during the grain‐filling period than during the period which bracketed silking. The results indicate a predominant source limitation for grain yield in the maize hybrid, and others of related genetic composition grown in short growing‐season environments similar to Guelph. Where this occurs, grain yield may be improved by increasing leaf area per plant, or by extending leaf area duration after flowering.