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Response of Sunflower to Plant Population¹

The cost of hybrid sunflower (Helianthus annuus L.) seed provides an incentive for reducing planting rates which, in turn, reduce plant populations. This research was undertaken to determine minimum populations needed for maximum yield and their effect on seed quality and head drying. Populations of oilseed and nonoilseed cultivars of 17, 25, 37, 49, and 62 thousand plants/ha were established at six locations in Minnesota. Soils were Typic Haplaquolls, Aeric Calciaquolls, Typic Eutroboralf and Udorthentic Haploborolls. Both oilseed and nonoilseed cultivars required the same populations for maximum yield. Minimum populations needed for maximum yield varied from 25 to 62 thousand plants/ha among locations. Differences in optimum plant populations among locations were attributed to soil, rain, and temperature. Yields were not depressed by populations up to 62 thousand. Optimum population for oilseed and small-nonoilseed cultivars was that which gave maximum yield because seed quality factors of test weight and/or oil percentage increased with population. Optimum population for large-nonoilseed cultivars was often less than that giving highest yield because the percentage of large seeds decreased with increasing population. As plant populations increased from 17 to 62 thousand plants/ha, head moisture percentages decreased from 68 to 50% at early harvest and from 43 to 20% at later harvest. Preharvest desiccant sprays reduced head moisture but did not alter the relationship between increasing population and decreasing head moisture. Increasing row spacing to conserve soil moisture between rows did not increase yield on a sandy soil.

Key Words: Helianthus annuus L. • Seed quality • Oilseed • Nonoilseed • Preharvest desiccation • Row spacing

² Agronomists, Univ. of Minnesota at St. Paul, Lamberton, Waseca, Grand Rapids, Crookston, Morris, and Crookston, respectively.

Received for publication June 4, 1979.