Corn Yield Response to Row Spacing and Plant Population in Iowa

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Parvej, M. R.
Wright, Emily
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Licht, Mark
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The Department of Agronomy seeks to teach the study of the farm-field, its crops, and its science and management. It originally consisted of three sub-departments to do this: Soils, Farm-Crops, and Agricultural Engineering (which became its own department in 1907). Today, the department teaches crop sciences and breeding, soil sciences, meteorology, agroecology, and biotechnology.

The Department of Agronomy was formed in 1902. From 1917 to 1935 it was known as the Department of Farm Crops and Soils.

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  • Department of Farm Crops and Soils (1917–1935)

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Corn (Zea mays L.) planted in narrow row spacing (<30-inch) with high plant population has become a recent interest in the US Corn Belt to increase grain yield. We evaluated the impact of row spacing and plant population on corn grain yield across 22 site-years in Iowa from 2009 to 2018. Experiments were designed as a split-plot with two row spacings, 20- and 30-inch, as the main-plot and three to four plant populations, ranging from 30,000 to 42,000 plants acre–1, as subplot. Grain yield was affected in 73% of the site-years: 13 site-years by row spacing, six site-years by plant population, and 2 site-years by the interaction of both. Corn in 20-inch rows yielded 5 to 19 bu acre–1 more in 11 site-years and 10 to 14 bu acre–1 less in two site-years compared to 30-inch rows. In both 20- and 30-inch row spacings, corn yield decreased linearly at 0.4 to 1.7 bu acre–1 per thousand increase in plant population in four site-years and responded quadratically with peak yield at around 36,000 plants acre–1 in two site-years. However, corn yield increased linearly at 2.0 to 3.1 bu acre–1 per thousand increase in plant population only when planted in 20-inch row in two site-years. When all 22 site-years were combined, yield was only affected by row spacing. Corn in 20-inch rows produced similar yield under low yielding environments and 8 to 10 bu acre–1 more yield under high yielding environments compared to 30-inch row spacing. Results suggest that farmers should move to 20-inch row spacing at yield levels greater than 235 bu acre–1.


This article is published as Licht, M.A., M.R. Parvej, and E.E. Wright. 2019. Corn Yield Response to Row Spacing and Plant Population in Iowa. Crop, Forage & Turfgrass Management 5:190032. doi: 10.2134/cftm2019.05.0032.

Tue Jan 01 00:00:00 UTC 2019