Analysis of Long Term Study Indicates Both Agronomic Optimal Plant Density and Increase Maize Yield per Plant Contributed to Yield Gain

Concurrent to yield, maize ( Zea Mays L.) plant density has significantly increased over the years. Unlike yield, however, the rate of change in plant density and its contribution to maize yield gain are rarely reported. The main objectives of this study were to examine the trend in the agronomic optimum plant density (AOPD) and quantify the contribution of plant density to yield gain. Maize hybrid by seeding rate trials were conducted from 1987–2016 across North America (187,662 data points). Mixed model, response surface, and simple linear regression analyses were applied on the meta-data. New outcomes from this analysis are: (i) an increase in the AOPD at rate of 700 plant ha −1 yr −1 , (ii) increase in the AOPD of 1386, 580 and 404 plants ha −1 yr −1 for very high yielding (VHY, > 13 Mg ha −1 ), high yielding (HY, 10–13 Mg ha −1 ) and medium yielding (MY, 7–10 Mg ha −1 ), respectively, with a lack of change for the low yielding (LY, < 7 Mg ha −1 ) environment; (iii) plant density contribution to maize yield gain ranged from 8.5% to 17%, and (iv) yield improvement was partially explained by changes in the AOPD but we also identified positive impacts on yield components as other sources for yield gain.