The tables down at the Chat 'n Chew Cafe are becoming less crowded in recent days as folks begin to head to the field in preparation for corn planting. Everyone remembers last year's rainy spring and delayed planting, and most don't want to get caught like that again. So, as the window opens for field work and planting, there will be a big rush to get the corn in the ground as fast as possible. While large acreages require early starts to planting, there are obvious risks of pushing corn planting too fast. Lowly agronomists like myself cannot stop the rush, but growers should be aware of the possible consequences of doing so and be prepared to diagnose uneven stands if they happen to occur.
Soil Compaction. Obviously, some fields will be worked on the wet side, resulting in soil compaction that can severely restrict corn root development later in May and early June. Subsequent shallow rooted corn is more vulnerable to summer dry spells, as evidenced by many Indiana corn growers in 1991 and 1995. Shallow rooted corn also tends to suffer more quickly from attacks by corn rootworm larvae when they are present in the field.
Since soil compaction is rarely uniform across a field, the effects of compaction usually are manifested by the tall corn/short corn syndrome as plants vary in their struggle to establish themselves. Shallow soil compaction can also cause uneven seeding depth during the planting operation if the planter's disc openers cannot penetrate the soil uniformly. Uneven seeding depth can lead to uneven germination and emergence, problems that can cause yield losses of ten percent or more.
If a field is planted on the wet side, sidewall compaction may result as the disc openers smear and compact the sides of the planter furrow. Development of the seminal (seed) roots can be easily restricted to the planter furrow, as can the first several sets of nodal (permanent) roots. Restricted root development can result in temporary nutrient deficiencies, stunting of the plant, and possible plant death.
Slow Germination & Emergence. Even though mid-April is upon us, average daily soil temperatures throughout the state are still mostly below 50 degrees F. For corn to germinate and emerge in seven days or less, soil temperatures at the four-inch depth should consistently average 50 degrees or higher.
When soil temperatures hover around 50 degrees F, sometimes dropping into the 40's, sometimes creeping into the low 50's, corn will take its sweet time germinating and emerging (Example from 1993). Instead of seven days to emergence, corn in cold soils may require two or three weeks to emerge. If temperatures vary throughout a field, then germination and emergence will be variable also, resulting in uneven emergence and yield losses of ten percent or more.
The risks associated with slowly germinating and emerging corn are mainly due to lengthier opportunities for exposure to possibly damaging soil insects and diseases, or even herbicide injury. If germination or emergence are slow and wireworms, seedcorn maggots, seedling blight, etc., happen to attack, the odds of survival by the corn seedling are much less than if germination and emergence occur at faster rates. Subsequent stands of corn may be uneven in their vigor and growth, resulting in yield losses of ten percent or more.
Bottom Line. If you elect to work or plant ground that is on the wet side, be prepared for the subsequent effects of soil compaction. If you elect to plant in soils that have not yet warmed consistently into the 50's or higher, be prepared for slow, possibly uneven, emergence that may also suffer from the effects of pests or herbicide injury.
Postscript: I would NOT favor altering seeding depth significantly to attempt to manage the soil temperature effect. Planting shallower to capture additional warmth increases the risk of seeds being placed into excessively dry soil or into soil that will subsequently dry rapidly. Planting deeper than normal to minimize the daily temperature fluctuation also places the seed into unacceptably cooler soil to begin with. I always favor a standard 1.5 inch seeding depth, with the understanding that, when necessary, I will plant deeper to reach uniform soil moisture.
Return to the the Chat 'n Chew Cafe.
The Corn Growers Guidebook , a WWW resource for corn management systems in Indiana and the eastern CornBelt.
Purdue University Agronomy Extension WWW Home Page.
Purdue Agronomy On-Line! , Purdue's Agronomy Department WWW Home Page.