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After a long winter and the arrival of spring, many growers want to get into the field. However, planting too early can have a negative impact on yield. It is important to plant according to soil temperature and conditions and be aware of potential issues caused by cold, wet soils.
Planting early can contribute to maximizing yield potential; however, planting into wet and cold field conditions may lead to poor emergence and less than ideal final plant populations. When planting corn, focus should be on examining existing field conditions, soil temperature and moisture, with less emphasis on calendar date.
Corn requires a soil temperature of 50°F to germinate and grow. Temperatures below the optimum can cause seeds to remain dormant and become more vulnerable to diseases, insects, and animal predators. Planting into cold and/or wet soils can lead to numerous problems.
Once planting commences, corn seed placement is critical to help maximize yield potential. Remember the following tips to help establish a good crop:
Do not plant too shallow. Planting less than 1.25 to 1.5 inches deep can result in rootless corn or root lodging. Shallow planting can also increase the risk of injury from some soil applied herbicides.
Do not plant deeper than necessary. When soil moisture is abundant, plant around 1.5 to 2 inches deep. When soil moisture is high, planting at depths of 2 to 3 inches can significantly delay emergence. If soil is dry and/or sandy, planting at 3 inches into moisture is less risky than planting shallow in anticipation of rain.
Planting when soil temperature and conditions are favorable is very important to give the crop the best chance of emerging properly and getting off to a good start. Although it is desirable to plant within the historic planting window (Table 1), rushing to plant in cold, wet conditions can lead to yield-reducing problems later.
The following describes the processes corn plants go through from emergence (VE stage) to stand establishment (V9 stage):
VE Stage. Emergence is achieved when the coleoptile reaches and breaks through the soil surface. Normally corn seedlings require about 100 to 120 GDUs to emerge, which under favorable conditions can be 4 to 5 days after planting.3 If cool or dry conditions exist, emergence may be delayed several weeks. At the VE stage, growth is also taking place below the soil surface as the nodal root system begins to grow. At about 6 weeks, the nodal root system will replace the work of the lateral seminal roots in supplying the plant with water and nutrients.
Table 1. USDA Corn Planting Dates in Minnesota and Wisconsin.
V1 Stage. The V1 stage is reached when the first leaf has fully emerged and the leaf collar is visible. The V1 stage typically occurs 3 to 4 days after emergence. The first leaf to emerge will have a rounded tip, while all later-emerging leaves will have more pointed tips.
V2 Stage. The V2 stage occurs when two leaves are fully emerged with collars visible. The V2 stage occurs typically 7 to 10 days after emergence or around 200 GDUs.4
V3 Stage. The V3 stage marks the end of the seed being the main food source and the beginning of the photosynthetic process. The V3 stage is reached at 10 to 20 days after emergence or at around 350 GDUs.4 At the V3 stage, the plant begins to rely more on the nodal root system as these roots form root hairs and continue to increase in size. Growth of the seminal root system has ceased.
V4-V6 Stage. During these stages the uppermost ear and tassel is initiated and kernel row numbers are determined. The growing point of the corn plant is near the surface. The V6 stage occurs at about 475 GDUs.4
Figure 2. Corn seedlings at V1 to V3 growth stages.