Uneven emerging corn seedlings

​2019 corn season in USA has started with unusual stress from wet fields in much of the corn growing areas. Not only was planting delayed but effects on seed environments has resulted in uneven emergence in some fields. Although nearly every plant in the single cross hybrid is genetically identical, too much water, or lack of water, seed quality, tillage, and soil compaction and inconsistent planting depth all may contribute to uneven emergence of these seed.  Multiple studies have attempted to evaluate the effect of uneven emergence on final yield.  One study published in 2012 in Journal of Plant Nutrition 35:480-496, 2012 (http://www.tandfonline.com/loi/lpla20) the yields and nitrogen uptake of plants from seeds planted between earlier planted seeds, finding that these individual plants yielded significantly less grain than adjacent plants of the same hybrid.
 
The multiple variables interacting with studies of delayed emergence makes the exact determination of effect emergence on final yield very difficult.  Shading of leaves by adjacent plants reduces photosynthesis.  Delayed silk emergence may miss pollen timing.  Competition for nutrients may be inhibited by earlier and greater root growth of adjacent plants.  Genetics of each hybrid may be affecting the reactions of each hybrid differently.  Although the exact affect in each hybrid-field environment should be expected to differ.
 
In the early 1970’s I was attempting to understand why stalk rot occurred in only some individual plants of a single cross hybrid and not in other adjacent plants.  If the cause was a fungus that was common, why did one plant develop stalk rot but not the genetically identical other plant?  My first hypothesis was that these were late emerging plants.  I marked some of these plants and followed their development though the season. Instead of developing stalk rot these plants had very narrow stalks, flowered later than adjacent plants, had deformed tassels with abnormally few glumes and very small, poorly pollinated ears. Not being sure that these plants were not inbred impurities in that hybrid, I intentionally planted seed between earlier emerged seedling.  This was done at the plant densities of that time with 5 commercial hybrids. The effects on plant develop was the same as observed the previous season, confirming that genetically identical plants are affected by interactions with adjacent plants.

My brief experiments were done with hybrids of the 1970s, commonly bred for much lower densities than is common in the USA today.  It should be expected that each hybrids reaction to delayed emergence will be different as well as each field environment will be different. We can acknowledge that uniform emergence is optimum but prediction of the exact result on final grain yield is complicated.