Abstract:

Maize (Zea mays ssp. mays) is a major staple crop, with the highest tonnage among cereal crops worldwide (FAO 2014). Over the past century, maize yields have increased over eight folds in the US central Corn Belt (from 1287 kg ha^-1 in the 1930s to 11,084 kg ha^-1 in 2017, http://www.fao.org, Duvick 2005b) due to a combination of genetic gain resulting from breeding efforts and improved management practices (such as application of synthetic nitrogen fertilizers, weed and pest control, increased efficiency of harvest equipment, etc.). A major management practice that contributed to the continuous yield increase is continual increases in planting density (from 30,000 plant ha^-1 or less in the 1930s to 80,000 plants ha^-1 or higher in the 1980s, Duvick 2005a, 2005b).