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Planting corn and soybean seeds too early and in poor soil conditions can have a negative impact on yield potential. Planting should be done according to soil temperature and soil moisture as opposed to the calendar date.
Soil temperature. Corn and soybean seeds will germinate and emerge slowly and unevenly when soil temperatures are less than optimal. Under cool soil conditions, seeds may remain dormant for several weeks, leaving them vulnerable to diseases, insects, and animal predators. For corn planting, soil temperatures should remain at or above 50° F. For soybean planting, soil temperatures should remain at or above 55 to 60° F.
Soil moisture. For planting, soil should be moist but not saturated. Planting into soils that are too wet has several downsides:
Figure 1. Restricted root growth in corn due to sidewall compaction.
Seedbed preparation. Tilling fields when soil is too wet can cause soil compaction, which can result in decreased germination, and restricted root growth and nutrient uptake. The majority of compaction takes place when equipment passes through a field. Consider staying out of the field if soil sticks to the tires or if equipment is leaving tracks deeper than 1 inch.
Planting depth. Soil temperature and moisture factor into planting depth. Corn seeds should be planted around 2 inches deep when soil moisture is adequate. Planting shallower than 1.25 inches can result in rootless corn or root lodging and can also increase the risk of injury from some soil applied herbicides. If soil is dry, corn can be planted deeper into moisture, at around 3 inches.
Soybean seeds should be planted at 1 to 1.5 inches deep and no deeper than 2.5 inches. Planting too deep can create added stress on the seedling and can inhibit emergence in stressful situations such as soil crusting and compaction.
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Nielsen, R.L. 2000. Corn growth & development: What goes on from planting to harvest? Purdue University. The Penn State agronomy guide, 2013-2014. Penn State University. 150305132301