Uneven seedling emergence can lead to grain yield loss.1,3 Delays of about 10 days can reduce yield 6 to 9% when compared to a full stand with normal emergence. Delayed to 21 days, yield losses can range from 10-22%, depending on the proportion of delayed emergers as compared to normal.3
Plants that are delayed in emergence, have a disadvantage when competing for light, water, and nutrients. The difference in growth stages that is critical to yield is around 2 leaves – beyond that, delayed emergers will likely be barren.1, 3, 9 Later silking plants attract corn rootworm beetles that can clip silks when feeding on pollen and there may not be be enough late tasseling plants in the field to provide adequate pollen for successful fertilization.
The primary factors affecting optimum germination and emergence include soil moisture, seed to soil contact, and soil temperature.1,3 Germination is triggered by absorption of water through the seed coat. Seeds need about 30% of seed weight in water for germination; less than that can halt or delay germination. Seed zone soil moisture needs to be evenly distributed and enough to make the seed bed not too wet, and not too dry.
Sufficient seed-to-soil contact is needed for all seeds to absorb moisture quickly and uniformly. Depending on the seedbed conditions, potential problems may include: seed-to-residue, seed-to-clod, seed-to-rock, and seed-to-air contact, none of which provide desirable results. Finally, temperatures greater than 50° F at a 2-inch depth are needed for timely germination and emergence.1 Soil temperature and variability are affected by soil characteristics, residue coverage, and seeding depth.1,2 Because exposed dark and dry soils warm more quickly, areas of heavy residue cover will harbor cooler soil temperatures beneath, and deeper planted seeds can be in slightly cooler seed zones.
Variable moisture in the seed zone at planting is the most common cause of uneven emergence according to the National Corn Handbook.2 Soil moisture and its distribution are affected by soil characteristics, tillage, weather conditions, and seeding depth.
Cool temperatures can lead to delayed corn germination and emergence. When soil temperatures are less than 55° F, germination can be greatly delayed.10 Corn can germinate in soil from 45 to 50° F, but due to the variability of soil temperatures, especially under residue cover, it is best to plant when average soil temperatures are 55 to 60° F.3 Imbibitional chilling injury can also occur under cool soil conditions. When seeds imbibe cold water at soil temperatures cooler than 55° F for an extended time, cell membranes can rupture causing plants to leaf out underground (Figure 1).9 Cool soils can also predispose corn seedlings to infection from fungi; the risk increases with a longer period in cool soils and under increased stress.
Improper seeding depth, seeds planted too deep or too shallow, can lead to numerous potential issues. Shallow planting can lead to early root lodging because of shallow nodal root development, injury to corn from pre-emergence herbicides, or drying of seed when moisture is not adequate. Deep planting can delay emergence especially during cool conditions of early planting and can reduce emergence when soil crusting is a problem, in heavy soils, or when heavy pest pressure is present. Shallower may be better on heavy soils, but beware of dry soils and an upcoming dry forecast. Optimal seeding depth can vary depending on soil conditions, and the environment before and after planting. Generally, it is around 1.5 to 2 inches, but there are circumstances where that may vary on the shallow or deep end by roughly one-half inch.11 Determining the correct corn seeding depth may be one of the most important decisions a farmer makes in the field during planting. This decision should be made in the field and based on current soil moisture and 5- to 10-day weather forecast, not from historical records.
Insect and disease pressure can be the cause of germination and emergence problems in corn. Seedling disease can be more severe in early planted corn and no-till or reduced tillage fields with heavy cover because of cool temperatures and in corn-on-corn situations due to increased inoculum pressure. Seed treated with Acceleron® Seed Treatment Products can not only help protect seed from soil and seed borne diseases including Fusarium, Rhizoctonia, and Pythium, but also help provide protection against wireworm, seedcorn maggot, white grub, and grape colaspis that can feed on seed kernels and destroy germinating seeds. Protection may be enhanced with the addition of Poncho®/VOTiVO® to further help protect seed from black cutworm and corn nematode pressure after root development initiation. Figure 2. Mesocotyl compromised due to soil crusting.
Soil and environmental conditions can lead to the coleoptiles splitting early causing leafing out below ground. Successful germination does not necessarily result in emergence (first leaves emerging through the soil surface). Exposure to light due to a cloddy or dry seedbed, sandy soil, or open slots in the soil can result in leafing out below ground. Soil crusting or furrow compaction can restrict elongation of the mesocotyl and cause corkscrewing (Figure 2) or leaves to emerge from the side of the coleoptiles. Injury from some types of herbicides under stressful conditions can also cause corkscrewing or leaves emerging from the sides of the coleoptile.
1 Nielsen, R.L. 2000. Corn growth and development. What goes on from planting to harvest? Purdue University. AGRY-97-07. www.agry.purdue.edu.
2 Carter, P.R., Nafziger, E.D., and Hicks, D.R. 1992. Effects of uneven seedling emergence in corn. National Corn Handbook. NCH-36. Purdue University.
3 Nielsen, R.L. 1997. Stand establishment variability in corn. Purdue University. AGRY-91-01. www.agry.purdue.edu.
4 Schwab, G. 2009. Avoiding anhydrous ammonia seedling injury. Corn & Soybean News. Volume 9, Issue 4. University of Kentucky. www.uky.edu.
5 Beegle, D.B., Roth, G.W., and Ligenfelter, D.D. 2007. Starter fertilizer. Agronomy Facts 51. Penn State University. http://extension.psu.edu.
6 Elmore, R. 2002. How does planter speed affect plant spacing? CropWatch. University of Nebraska. (published in Corn Production, Iowa State University. www.agronext.iastate.edu).
7 Jasa, P. 2007. Increased planting speed can cost yields. Nebraska crop production & pest management information. CropWatch. University of Nebraska. http://cropwatch.unl.edu.
8 Nielsen, R.L. 1993. Planting speed effects on stand establishment and grain yield of corn. Summary of 1993 on-farm trials. Purdue University. AGRY-94-02. www.agry.purdue.edu.
9 Elmore, R. 2012. Imbibitional chilling and variable emergence. Integrated Crop Management News. Iowa State University. www.extension.iastate.edu.
10 Robertson, A. 2006. Corn seedling health and stand establishment. Integrated Crop Management IC-496(12). www.ipm.iastate.edu.
11 Thomas-Murphy, J. 2014. How does corn planting depth affect stand establishment? What’s Cropping Up? Cornell Field Crops Newsletter. http://css.cals.cornell.edu. Web sources verified 1/12/15.