Much needed rainfall received last week helped bring on the emergence of corn and soybean plants across the region. Many corn fields have taken on a greenish hue seen when driving on the road parallel to the corn rows; a sideways glance when traveling perpendicular to the planting direction reveals the definite lines of rapidly growing corn seedlings. Variable soil moisture conditions have resulted in some uneven emergence, but overall, stands look pretty good.

We would all like to see every plant pop out of the soil on the same day, but that rarely, if ever happens.  So, what does uneven emergence cost?

Research, conducted at the universities of Illinois and Wisconsin by Extension Corn Specialists Paul Carter and Emerson Nafizger, showed that emergence delays of about 10 days scattered throughout the field reduced yield 6 to 9 percent compared to full stands of normal emergence.  Some suggest a 1 percent loss per day of delayed emergence, depending on the proportion of delayed emergers to normal emergers. If it takes 3-4 days for an entire field to emerge, what will be the yield impact? Naturally, many variables are involved.

The reason for the detrimental effect of delayed emergers is that they simply cannot compete with older, more established plants for sunlight, moisture and nutrients. The delayed emergers will typically become stunted in their growth and rarely produce a harvestable ear. In fact, some of the latest emergers may actually perform more like a weed, sucking soil moisture and fertility from neighboring plants.

To determine the severity of the problem in your field, compare growth stages of normal and delayed emergers. From Purdue’s Bob Nielsen’s observations in the field, a growth stage difference of two leaves or greater between adjacent plants will almost always result in the smaller (younger) of the two being barren at the end of the season. 

Nielsen has stated that the only conditions you need for perfect emergence in a corn field are adequate soil moisture, soil temperature, and seed-to-soil contact. Pretty simple, right? In practice, however, if one or more of these factors is limiting, the resulting germination or emergence is uneven. 

The primary causes of delayed seedling emergence in corn include soil moisture variability within the seed depth zone and poor seed to soil contact due to cloddy soils, inability of no-till coulters to slice cleanly through surface residues, worn disc openers, and misadjusted closing wheels. 

Other causes include soil temperature variability within the seed zone, soil crusting prior to emergence, occurrence of certain types of herbicide injury, and variable insect and/or soil-borne disease pressure. 

Hindsight I know, but seeding depth decision should be made in the field, not in the shop or from last year’s records. The correct seeding depth for any given field should be based on its current soil moisture conditions and the 5- to 10-day weather forecast. 

For example, if the soil is dry down to 1.5 inches and the short-term forecast calls for continued dry weather, do not hesitate to plant at 2 or 2.5 inches. With such dry soil conditions, the risk of germination problems is greater for shallow planting than for deeper planting. 

We saw lots of dust flying during corn planting in April. Looking back, was that last tillage pass beneficial in breaking up soil clods? Or, was an extra quarter to half inch of moisture lost to the wind? 

Readers with questions or comments for Roger Bender may write to him in care of this publication.