April 12, 2013

Q: Can I increase irrigated corn population and yield by planting in 15-inch rows? If so, how much can I increase population?

A: We did a study in northeast Nebraska a few years ago to compare 15- and 30-inch row spacings. Over three years we saw an average yield increase of 4% (two years at 7% and one year at 0%). My guess is that dropping from a 20-inch to a 15-inch row spacing might show a slight increase, but not as much as we found. Our study also looked at populations and nitrogen rates. There was not much difference between the two row spacings at normal populations, but where we overplanted (35,000) the 30-inch rows did worse.

Charles Shapiro
Extension Soil Scientist - Crop Nutrition

UNL Research Recap

UNL soil scientists conducted field experiments for three years (1996-1998) comparing the effects of 30-inch versus 20-inch row spacing, three plant densities, and four nitrogen rates on crop performance. Populations of 25,000, 30,000 and 35,000 plants per acre and nitrogen rates of 0, 75, 150 and 225 lb per acre were tested in a silty clay loam soil.

• Decreasing row spacing from 30 inches to 20 inches resulted in 4% more grain yield.
• Nitrogen application resulted in mean increases of 22% more biomass and 24% more grain yield.
• Plant N concentration, biomass, and grain yield were not affected by plant density.
• Reduced row spacing, but not increased plant density, resulted in more crop N uptake and more grain yield. N use efficiency was increased with narrower row spacing when plant density was at the highest level tested.
• Grain yield was not affected by increasing plant density above 25,000 plants per acre, but was greater with narrow row spacing. Other research has shown that increased plant density with narrow row spacing can contribute to reduced early season weed competition and increased early plant growth.

To read more about this study by Shapiro and Charles Wortmann, both soil scientists at UNL, see the April 11, 2006 article in the Agronomy Journal.