Sunflower Cultivar Performance as Influenced by Soil Water and Plant Population1

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Abstract
Information on the yield performance of sunflower (Helianthus annuus L.) as related to a range of soil water potential in the near‐optimum range has not previously been reported. Previous studies of sunflower plant population density effects on yield have lacked agreement. In this study three sunflower cultivars (‘Peredovic’, ‘894’, and ‘Northrup King 212’) were tested for response to soil water potential at Oakes, North Dakota and for response to population density at Carrington, North Dakota (irrigated) and Fargo, North Dakota (dryland). Yield was higher if the soil water potential in the root zone, as measured by commercial tensiometers, was limited to values of ‐20 cbar and ‐40 cbar and was lowered if the root zone water potential was allowed to drop to ‐75 cbar. There was no significant difference in seed yield between populations at thinning of 49,400, 59,300, and 69,200 plants/ha. A comparison of harvest methods at Oakes indicated that a number‐of‐heads harvest method increased yield estimates by 20% compared to an area harvest method. This comparison also showed that the harvest method used did make a significant difference in yield results obtained from the water potential experiment. It is hypothesized that harvest method may have influenced previous sunflower population density experiments similarly.

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