Utility of Higher Plant Densities for Corn Performance Testing

We grew 84 different corn ( Zea mays L.) performance tests in paired‐density comparisons averaging 51 600 and 64 500 plants per hectare over a 9‐year period to examine the utility of higher plant densities for corn performance tests. The higher density reduced yield test means from 76 to 73 q/ha, increased ranges among hybrids from 40 to 44 q/ha, and decreased hybrid F values for tests from 3.6 to 3.2. Broken stalk test means increased from 10 to 12%, ranges among hybrids increased from 35 to 39%, and hybrid F values for tests increased from 2.5 to 2.9 with the higher density. Dropped ears showed a large period‐of‐years effect due to effective selection. Testing at above optimum plant densities increased barrenness, stalk breakage, and ear droppage; it also increased the range among entries, thereby increasing the ease of selection against these traits. We analyzed 5 years' data from 250 strip tests comparing two widely grown hybrids at three plant densities and found that increased densities reduced number of tests needed to differentiate the hybrids. On the average twenty strip tests with alternate check strips grown at plant densities at or above 56 000 plants per hectare successfully differentiated (P = ca. 0.05) 7% yield at 75 q/ha average yield, 1.8% broken stalks at 5% average broken, and 2.4% root lodged at 2.5% average lodged; the two hybrids did not differ for dropped ears. Superior commercial hybrids resulted via higher plant density testing.