With the tax filing deadline rapidly approaching and morning low temperatures this past week in the mid- to low 20 degrees, we expect that many growers are getting just a bit anxious to get to the field to start planting corn. Thankfully, the ten day forecast is finally calling for a much higher average temperature beginning next week. Warmer temperatures are important for corn planting since the key to achieving top yields is obtaining a uniform emerging stand. Corn germination begins once the soil temperature at a 2 to 3 inch depth reaches 50°F. Soil temperature is especially critical in no-till planting situations. Since so many growers now have both a cover crop on their fields and substantial amounts of crop residue, the soil remains cooler than when the soil is worked even by disk or turbo-till. In addition, many locations in Delaware have received 2.5 to 3 inches of rainfall already this month. Moist to wet soil conditions mean that it will take longer for the soil to warm up, even with clear skies and warmer air temperatures.
Corn that takes two to three weeks to emerge often has a lower yield potential and has much greater variability in the growth stage of seedlings. When seedlings differ by two or more leaf stages (a two fully emerged leaf plant versus a four fully emerged leaf plant), the smaller plant can act more like a weed to the corn crop than a contributor to the field’s yield potential. In addition, the smaller, later emerging plants allow more sunlight to reach the soil surface, which can stimulate weed germination and competition if the weed control program is not adequate or fails.
There are some management techniques growers can use to make the most of the upcoming favorable weather period, even with the corn planting season getting a bit of a late start. Using row sweeps or row cleaners to remove the stubble from over the row to allow direct sunlight on the soil surface that can help warm the seed row. Another technique is use starter fertilizer in a band near the seed to encourage rapid rooting and quick nutrient uptake. On sandy soil, take care to avoid fertilizers with too high a salt index to prevent damage to the stand. Still, applying enough starter fertilizer to carry the corn crop to sidedress time can help maximize yield potential. We recommend 2 × 2 placement of starter fertilizer over the use of in-furrow (“pop-up”) starter fertilizers. Placement of the fertilizer within the furrow increases the risk of damage to the seed and/or emerging seedling. High salt concentrations can damage and/or dry out emerging roots, leading to uneven emergence, which can potentially reduce yields.
Growers should also consider field selection to maximize yields over the whole operation. Consider planting those fields that have the best drainage and are sandier or darker with organic matter before other fields. Sandier fields and fields with black soils tend to dry more quickly and, therefore, also warm faster; these fields will pick up more heat during the sunny and warmer weather that is forecast for next week. Fields that are more open to the wind or have less shading from woods at the field edge will also warm faster.
Once the soil temperature climbs into the 60 degree range, growers should consider planting their most productive fields because emergence will be relatively rapid and even at that point. This will ensure that a grower’s most productive fields have the greatest yield potential and potential profitability.