Considerations for Early Planting of Corn and Soybean

 

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Plant when Soil Conditions are Optimal

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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.

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  • For corn planting, soil temperatures should remain at or above 50 °F.
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  • For soybean planting, soil temperatures should remain at or above 55 to 60 °F.
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Soil moisture. Soil should be moist but not saturated for planting. Planting into soils that are too wet has several downsides:

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  • Prolonged exposure to soggy, wet soils deprives the seed of oxygen needed for germination and plant growth and can increase the incidence of disease.
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  • Disk openers slicing through wet soil can create sidewall compaction in the seed zone, which can restrict root growth. Down pressure on coulters should be regulated to establish proper seeding depth dependent on soil moisture.
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Seedbed preparation. Tilling fields when soil is too wet can cause soil compaction, which can result in decreased seedling germination and restricted root growth and nutrient uptake.

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  • The majority of soil compaction takes place when equipment passes through a field.
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  • Consider staying out of the field if soil sticks to the tires or if equipment is leaving tracks deeper than 1 inch.
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Planting depth. Soil temperature and moisture factor into planting depth.

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  • Corn seeds should be planted around 1.5 to 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.
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  • 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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Starter fertilizer. Early planted corn can benefit from starter fertilizers. The greatest benefits from starter fertilizer occur in cool, wet soils when seedling development will be slower.

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Benefits of Early Planting

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Benefits of early planting of soybeans. Earlier planting dates typically have the potential to produce higher soybean yields due to the following factors:

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  • Soybean plants can produce larger canopies earlier in the season (Figure 1), which can intercept more light leading to greater overall photosynthesis and conservation of soil moisture, which is critical during reproductive growth periods.
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  • A longer growing season, which can result in an increase in the number of nodes on the main stem and potentially more pods per plant.
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  • A lengthened reproductive growth period due to earlier flowering and increased crop growth rate during pod set, which can lead to a greater seed filling rate.
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Figure 1. Comparison of the development of soybeans planted at four dates. Photo courtesy of Dr. James Specht, University of Nebraska-Lincoln. Source: Bastidas, A.M. et al. 2008. Soybean sowing date: the vegetative, reproductive, and agronomic impacts. Crop Science. vol 48: 727-740.
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Soybean planting dates. The University of Nebraska recommends to plant your soybeans as close to May 1st as possible. Approximately 1/2 bu/acre/day of yield potential can be lost for every day after May 1 that planting occurs.1 Benefits of early planting of corn. Planting corn early can result in the following benefits:

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  • A longer growing season for plant development with earlier canopy closure for soil moisture conservation.
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  • Reduced pest pressure throughout the growing season.
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  • An earlier pollination period to avoid the heat that commonly occurs during this critical growth stage.
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  • Improved standability due to shorter plant height.
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  • Earlier maturity and faster dry down.
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These benefits are lost with late planting, with a commensurable loss of potential yield to the magnitude of 1 to 2 bu/acre/day past the optimum planting window.2

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Corn planting dates. In general, the optimum planting period for corn in Nebraska is between May 1 to May 15. This window can be adjusted slightly earlier for southeastern and south central Nebraska and slightly later for northern Nebraska. When conditions are permittable, farmers may be able to capitalize on the yield benefits by planting earlier, but remember to consider the early planting restrictions in your crop insurance policy (which is April 10th or April 15th depending on location), which is the earliest date of planting where you can still qualify for a replanting payment in the event of a crop loss.

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