Production Resources

Ensuring corn emerges uniformly is the first step in maximizing yield potential.

Why corn emerges unevenly

The most common reason for uneven corn emergence is soil moisture. Soil moisture in the seed zone can differ because of variations in soil type and topography, as well as uneven distribution of moist and dry soils due to secondary tillage. Cloddy seedbeds, caused by working the ground when it is too wet, can result in poor seed-to-soil contact, allowing some seeds to germinate while others are too dry.

Another factor affecting corn emergence is soil temperature. Seed depth soil temperatures can vary if crop residues are not evenly distributed, if seed depths vary and if soil within a field varies in type and topography. Corn may also emerge non-uniformly because of variable soil crusting, herbicide injury or insects and diseases.

Impact on grain yields

Competition from larger, early emerging plants will decrease the yield of smaller, later-emerging plants. Research out of the University of Illinois examined the effect of non-uniform emergence on grain yield. Plots were planted by hand and consisted of uniformly planted plots on three separate dates, and various combinations with certain parts of the plot seeded later to simulate delayed emergence.

When looking at within-row emergence patterns, a definite yield decrease was seen when plants emerged later than their neighbour (Table 1).

Table 1: The effect of planting date and uniformity of emergence within-row on corn yield. (Average of seven locations in Illinois and Wisconsin from 1986-1987). Source: Nafziger, Carter and Graham, Crop Science 31 : 811 - 815 (1991).

The treatment 3E:1M consisted of one plant in every four being planted 10 days later. The result is a decrease in yield of 12 bu/acre (176 bu/ac) compared with the plots where all plants emerged uniformly on the early planting date (188 bu/ac). This yield loss was similar if the entire stand was delayed 10 days. Similar results are seen when emergence (planting) was delayed by three weeks, where a decrease in yield of 20 bu/ac was seen compared to the plots where all the plants emerged uniformly on the early planting date.

What to look at before and after planting

Careful planter preparation and pre-planting management are crucial factors affecting uniformity of emergence. On the planter, factors to check include:

• Opening discs are aligned
• Ensure planter is level
• Properly adjust seed firming wheels – see Figure 1.
• Proper seed depth placement

Figure 1: Seed rows were unable to close, most likely due to seed firming wheels not being adjusted properly and possibly wet soil conditions at planting.

Pre-planting management factors to check include:

• Residue – is it bunched?
• Ensure field is not too rough

During planting, ensure speed is suitable for the field conditions. If field conditions are poor and planting is done at higher speed, the planter bounce can cause seed depth variability. If one seed out of four is placed out of moisture and it doesn’t rain for a week, a yield decrease may result.

After the crop is up and growing, examine to see if the corn plants are all at the same leaf stage. If there are plants that are 1-2 leaves behind their neighbours, it could indicate problems with emergence. Nothing can be done for this growing season, but knowing what caused the variability can help with future corn planting operations.

Figure 2: Uneven emergence in corn. Smaller corn plants act as a weed to the more mature corn plants and may "rob" nutrients and water from other plants.