Plant Density Effects on Yield & Yield Components of Maize Hybrids That Purportedly Differ in Response to Plant Density.

In an effort to increase yield seed companies are breeding hybrids to tolerate high plant populations (>93,000 plants ha^-1) and encouraging producers to plant high seeding rates to take advantage of this characteristic. Our objective was to compare yield and yield components of 2 hybrids, one marketed as “highly-responsive” (RHy) to high plant populations and the other considered “normally-responsive” (NHy), across a range of seeding rates (61,750 to 113,620 seeds ha^-1 in 4 increments of 17,290 seeds ha^-1) in 76 cm rows. This study was conducted in 2013 at 4 locations varying in soil type, management practices, and weather conditions. Final populations ranged from 91-98% of intended seeding rate across locations, with 2% greater success at the lowest seeding rate compared to the 3 higher rates at 2 locations, but no differences at the other 2 locations. Percent of intended seeding rate for RHy and NHy differed by less than 4%. At silking (R1), RHy had 80 to 100 fewer potential kernels ear^-1 than NHy at all locations and seeding rates. Increased seeding rate decreased potential kernels ear^-1 from approximately 750 to 700 in a curvilinear fashion at 2 of 4 locations, but no difference due to seeding rate occurred at the other 2 locations. At grain blacklayer (R6), RHy had about 30 fewer kernels ear^-1 than NHy averaged across all seeding rates and 3 locations, but no difference at location 4. Kernels ear^-1 decreased from approximately 600 to 440 as seeding rates increased for both hybrids at all locations. The 2 hybrids did not differ in kernel weight at 3 of 4 locations when averaged across all seeding rates. However, at one location RHy had a higher kernel weight than NHy at 61,750 seeds ha^-1, but they did not differ at higher seeding rates. At all locations kernel weight decreased in a curvilinear fashion as seeding rate increased. Both hybrids yielded the same at 3 of 4 locations irrespective of seeding rate. Predicted maximum yield was 10,483, 13,809, and 12,428 kg ha^-1 at ≤ 61,750, 85,956, and 88,673 seeds ha^-1 for the 3 locations. At the other location NHy yielded 753 kg ha^-1 more than RHy at the lowest seeding rate 61,750 seeds ha^-1, but no greater at the higher seeding rates. Overall, the two hybrids examined responded similarly to plant population despite marketing claims of high differing responsiveness to high populations, and optimum yields occurred at seeding rates ≤ 88,673 seeds ha^-1.