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Corn seedlings may emerge at different times if soil is either too dry or too wet shortly after planting. Soil moisture can vary within a field due to differences in soil characteristics or topography. Planting at an uneven seeding depth or planting too shallow can lead to uneven soil moisture in the seed zone. A planting depth of less than 1.5 inches can increase the risk of uneven germination and emergence due to drying of surface soils.2Soil temperature. It takes about 119 growing degree days for corn to emerge. Corn emergence occurs in 7 days or less when soil moisture is adequate and soil temperatures are in the mid-50 °F or warmer.2 When soil temperatures are less than 50 °F, corn germination and emergence occurs more slowly and unevenly. Variation in soil temperature in the seed zone can be caused by surface residue, differences in soil texture and color, soil drainage, and uneven seedling depth.
Table 1. Relative yield potential for corn with different planting dates and populations. 4
Sources: 1 Elmore, R. and Abendroth, L. 2006. Yield effect of uneven corn heights. Iowa State University Agronomy Extension. http://www.agronext.iastate.edu. 2 Nielsen, R.L. 2010. Requirements for uniform germination and emergence of corn. Purdue University. http://www.agry.purdue.edu. 3 Nielsen, R.L. 2010. Visual indicators of germination in corn. Purdue University. http://www.agry.purdue.edu. 4 Elmore, R. and Abendroth, L. 2009. Assessing corn stands for replanting. Iowas State University. Integrated Crop Management News. http://www.extension.iastate.edu Carter, P. R., Nafziger, E.D., and Lauer, J.G. Uneven emergence in corn. North Central Regional Extension Publication.