Submitted to: Crop Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 25, 2006
Publication Date: May 1, 2006
Citation: Ray, J.D., Fritschi, F.B., Heatherly, L.G. 2006. Large application of fertilizer n at planting affects seed protein and oil concentrations in the early soybean production system. Field Crop Research. Vol 99: 67-74 Interpretive Summary: Soybean is primarily grown as a source of high protein meal. In order to achieve a high protein meal, soybean requires a tremendous amount of nitrogen. The soybean plant obtains nitrogen from two primary sources: from the air (symbiotic nitrogen fixation) and from the soil (inorganic nitrogen). This study was undertaken to examine the effect of nitrogen source on the relative amounts of protein and oil in the seed by adding large amounts of fertilizer nitrogen to soybean. The nitrogen fertilizer decreased protein concentration and increased oil concentration resulting in an overall decrease in the protein to oil ratio. However, the total protein per acre increased because of increased seed yields as a result of the added nitrogen fertilizer. Understanding the underlying mechanisms governing the changes in protein and oil concentration as a result of nitrogen source may open avenues of research to develop cultivars with greater protein concentrations.
Technical Abstract: An inverse relationship between soybean [Glycine max (L.) Merr.] seed protein and oil concentration is well documented in the literature. A negative correlation between protein and yield is also often reported. The objective of this study was to determine the effect of high rates of N applied at planting on seed protein and oil. Nitrogen was surface-applied at soybean emergence at rates of 290 kg ha-1 in 2002, 310 kg ha-1 in 2003, and 360 kg ha-1 in 2004. Eight cultivars ranging from Maturity Group II-IV were evaluated under the Early Soybean Production System (ESPS). However, not all cultivars were evaluated in all three years. Glyphosate herbicide was used in all three years and a non-glyphosate herbicide treatment was applied in 2002. Cultivars grown in 2003 were also evaluated under an application of 21.3 kg ha-1 of Mn. All cultivar, herbicide, and Mn treatments were evaluated in irrigated and nonirrigated environments with fertilizer N (PlusN treatment) or without fertilizer N (ZeroN treatment). When analyzed over all management practices (years, cultivars, herbicide, and Mn treatments), the PlusN treatment resulted in a significant decrease in protein concentration (2.7 and 1.9%), an increase in oil concentration (2.2 and 2.7%), and a decrease in the protein/oil ratio (4.7 and 4.6%) for the irrigated and nonirrigated environments, respectively. However, the overall protein and oil yield increased with the application of fertilizer N at planting (protein: 5.0% irrigated, 12.7% nonirrigated and oil: 9.9% irrigated and 18.9% nonirrigated). These increases were due to the increase in seed yield with the application of large amounts of fertilizer at planting. Additionally, a significant correlation (r=0.45, P=0.0001) was found between seed protein concentration and seed yield. No significant correlation was found between seed oil concentration and seed yield. The data demonstrate the inverse relationship between protein and oil and indicate that large amounts of N applied at planting do not change this relationship.