During the last few days, observations of fields of early planted corn have revealed spotty and poor emergence, reports Jason Van Maanen (Veritas Chatham). These are not crop failures; it’s more a “the stands are ok but they should be better” situation. Here is some information on how corn emerges and some of the possible factors that are causing less than ideal stands.
Poor Corn Emergence
For successful stand establishment of a corn crop, successful emergence of the seedlings is the key. Seedling emergence occurs as a result of elongation of the mesocotyl that elevates the coleoptile or “spike” toward the soil surface. If successful, the appearance of the coleoptile at or near the soil surface is synchronized with the emergence of the first true leaf from inside the coleoptile. If mesocotyl elongation and/or coleoptile emergence are compromised, the emergence of the leaves from the coleoptile may occur underground and remain trapped by the soil.
Poor emergence may be caused by either a failure of the mesocotyl to successfully elongate and/or the soil restricting successful penetration of the coleoptile. In extreme cases, elongation of the mesocotyl fails completely resulting in a corkscrew appearance.
The effect on grain yield will depend on the initial seeding rate, the severity of the problem and growing conditions the remainder of the season. Very few affected fields, however, have merited replanting.
Often, more than one of the following factors exist in a problem field and usually interact with each other to amplify the problem.
Restricted Emergence: Corkscrewed mesocotyl/coleoptile development can result when the coleoptile encounters resistance as the mesocotyl elongates. Soil crusting, a compacted soil or a cloddy soil surface can cause such resistance. While the crusting observed is not severe, the dry soil conditions that made tillage easy, combined with the locally heavy rains of the past few weeks and current dry conditions have created a light to moderate crust on some soils.
Cold Soils: Cold soils and/or wide fluctuations in soil temperatures throughout the day during the emergence process are also thought to be major contributing factors to the development of corkscrewed mesocotyls. The exact minimum soil temperatures that can cause such corkscrewed development are unknown, but clearly it is not uncommon during the last month for daily soil temperatures to dip as low as 5o C during April and early May. Furthermore, bright sunny days can elevate bare soil temperatures quite high but still drop quite low the following night causing a large daily fluctuation in soil temperatures. Dry soils are more prone than wetter soils to large swings in daily soil temperatures.
Imbibing Damage vs. Cold Temperatures: Cold temperature injury that results in corkscrewed mesocotyls is not exactly the same as that which is referred to as “imbibitional chilling” injury. The latter refers to cold injury to the seed during the first 24 to 72 hours after planting when the seed imbibes (absorbs) water. Imbibition of water causes the seed to swell. If seed cell tissue is very cold, it may become less elastic and thus may rupture during the swelling process. The most common symptom of such imbibitional chilling damage to seed cell tissue is visibly swollen seed with little to no evidence of germination progress. Conversely, seedlings with corkscrew mesocotyls germinate successfully. The cold temperature damage occurs slightly later, during the early stages of mesocotyl elongation and affects the mesocotyl tissue, not the seed tissue.
If emergence issues are observed have a closer look at the seed as one or both of these factors may be at play in the field. Also, conduct a population count to verify that the final population is still viable. Every year, there is corn that does not emerge. As long as the final population is good and the stand is healthy, there is no reason to be concerned about replanting. If you have any questions, contact your Veritas agronomy team.
Sources: Bob Nielsen, Purdue University