Effects of Nitrogen, Phosphorus, and Plant Density on Sunflower

It is generally recognized that appropriate plant density and appropriate fertilizer application to deficient soil are necessary for optimum yield of crops. These variables also affect the quality of some crops. There is limited research data on the effects of these variables on yield and quality factors of oil and confectionery cultivars of sunflower (Helianthus annum L.) grown in North Dakota. The objectives of this research were to determine the effects of three rates of nitrogen fertilizer, two rates of phosphorus fertilizer, and three plant densities upon seed yield, head size, oil concentration of oil cultivars, and seed size of confectionery cultivars. Nitrogen fertilizer increased seed yield, head size, oil yield from oil-type cultivars, and percentage of large size seeds from confectionery cultivars. However, N reduced oil concentration of oil-type seeds and percentage of medium size seeds of confectionery cultivars. Yield response to nitrogen was obtained at all locations because soil tests for nitrate-N to a 61 cm soil depth were less than 60 kg/ha at planting time. Phosporus fertilizer failed to increase seed yields in 10 of 12 trials and had little effect on size of confectionery seeds and oil concentration of oil-type seeds. Lack of response to phosphorus cannot be explained by soil test data. Increasing plant density increased seed yield, yield of oil from oil-type sunflower, and percentage of medium-size seeds from confectionery cultivars. Increasing plant density reduced head size and percentage of large-size seeds of confectionery cultivars. Percentage of small sized confectionery seeds was increased by increasing plant density and decreased by increasing rate of nitrogen fertilizer. Results of this study show that nitrogen and plant density have a relatively large effect on seed yield and a smaller effect on oil concentration and seed size.