Corn genetics and planting rates have changed a lot in the last 50 years. Breeding and selection of hybrids when planted in the USA Midwest at 22000 plants per acre required different genetics than when planted at 36000 plants per acre. Plants had more kernels supplied by more photosynthesis per plant. Higher densities with those hybrids would certainly develop the photosynthetic stress dynamics resulting in stalk rot because of insufficient carbs to supply both the grain and roots. More plants per acre, and slightly smaller ears per plant allowed a total of more grain, compensating for the reduction in photosynthesis per plant. On the other hand, these types of hybrids are more reliant on getting maximum number of productive plants. This is not only the necessity of high number of germinating seed but also that the seedling emerge uniformly. This was discussed in Corn Journal on 3/10/2016.
40 years ago, when pursuing the question of why one plant died early with stalk rot and the adjacent plant did not, I hypothesized that the dead plant was that one emerged late as a seedling. When most of the plants in the test plots showed their 5th leaf, a tag was put near those that had only 3 leaves and another marking those with only a spike. Notes were taken of these plants and their adjacent plant during the season. At pollination, it was clear that even those tagged at three leaves were not silking in time with adjacent plants and tended to have more slender stalks. Many of those tagged as spiking no longer were present, but those that survived were far off in pollination timing, had very small, narrow stalks and, eventually, small tassels. Ears were harvested at end of season and kernel numbers were counted. Those tagged with three leaves had only 20% of kernels of adjacent plants and those tagged as spike only were barren. Delayed emerging plants did not develop stalk rot but clearly the delay affected yield.
To eliminate the possibility that these delayed plants were not ‘selfed’ inbreds instead of hybrid plants, an experiment was performed the next season to confirm that emergence delay was the main factor. Seed was planted with twice the normal plant-to-plant spacing. When those seedlings spiked, the same hybrid seed was planted between the seedlings. This would be an unusual delay, but the effect was the same as the first observation. Barren plants, skinny stalks, small tassels were characteristic of the delayed emergence. Apparently, plant competition for late emerging plants has a drastic affect.
Others have done similar experiments before and after these done by a young guy beginning to learn about corn. My conclusion was that individual plants developing stalk rot were not the late emerging ones and that uniform emergence was an important factor in corn yields. Also, it was interesting that those late emergers could be confused with selfs, as confirmed by the fellow who normally evaluated hybrid purity in winter growouts. That eventually led to developing a different purity test method.
My experiments were done in the 70’s with hybrids and plant densities common at that time. It would be useful if similar experiments were done with more recent hybrids selected for consistent ear development at the higher plant densities used today. It is notable that experiments done by others have shown that among germination test methods, the cold test is the best predictor of field emergence and that it accounts for about 70% of differences among seed lots in field emergence.
About Corn Journal
The purpose of this blog is to share perspectives of the biology of corn, its seed and diseases in a mix of technical and not so technical terms with all who are interested in this major crop. With more technical references to any of the topics easily available on the web with a search of key words, the blog will rarely cite references but will attempt to be accurate. Comments are welcome but will be screened before publishing. Comments and questions directed to the author by emails are encouraged.