What will 15 inch row wheat yield?  Because some Ohio wheat producers are interested in growing soft red winter wheat in 15-inch rows in order to utilize a more precise planting implement, reduce equipment inventory, Modify Relay Intercrop (MRI) soybeans into wheat (done when wheat is headed out), sow cover crops or establish a forage crop; wheat yield in a 15-inch row is important in evaluating any row spacing change.  

Wheat variety yield in 15-inch rowsResearch done by Beuerlein & Minyo in 2008 with 3 wheat trials found 7.5 inch row spacing to out yield 15 inch row spacing  by  about  7.2 % or 6.6 bushels per acre (bu/ac). Read this research report. In 2009 and 2010, Lee and Herbek, of the University of Kentucky,  grew three varieties of wheat at two locations in 15-inch and 7.5-inch rows. Varieties tested were known to be prolific (varieties produce a lot of tillers). Yields ranged from 70 to just over 120 bu/ac. In two of the environments, there were not any differences in yield between 15-inch and 7.5-inch rows. In the other two environments, wheat yields in 15-inch rows were about 8.5% less than wheat yields in 7.5-inch rows. To read the entire research summary. Johnson, in 2006 and 2007, examined wheat yield in 7.5 and 15 inch row wheat in Ontario.  Wheat yields were reduced from 5 to 8 percent when wheat rows were widened. For more information on this trial.  

In 2011, Minyo evaluated wheat varieties in a 15 inch row spacing over yield at the Bucyrus location of the Ohio Wheat Performance Test.  Varieties selected were in the top half of the 2010 Ohio Wheat Performance Test. The average yield for this plot of 25 varieties was 93.2 bu/ac with a range from 88.1 to 99.8 bu/ac.  Seeding rate was 25 seeds per foot of row for all varieties.

All of the wheat varieties in the 15 inch row trial were also in the 2011 - 7.5 inch row trial at Bucyrus (70 varieties tested) which averaged 98.3 bu/ac with a range of 107.4 to 82.1 bu/ac . It should be noted that a statistical comparison between the two wheat row spacing’s cannot be made from the 2011 study at Bucyrus. Therefore, only relative yield of wheat in 15 inch rows by variety is reported in the linked table. A further limitation of this data is that it represents only one location and one year. The Ohio Wheat Performance Test is available here

If farmers wish to MRI, double crop or sow a forage/cover crop into the wheat, then in addition to yield in a 15-inch row, maturity and plant growth habit (reported in another article at http://crawford.osu.edu  are very important to the establishment and growth of the subsequent crop from the aspect of available light.  For example soybeans interseeded into wheat with a dense canopy (>3 on scale used by Beuerlein and Minyo ) and prior to head emergence may  become spindly and may  be of low vigor. Light available for the interseeded crop will be a function of heading date (maturity), plant growth habit, row spacing and yield.