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Soil temperature is key factor in deciding when to plant

Soil temperature is key factor in deciding when to plant
The effects of planting into cold soil temperatures begin before the plant germinates.

By Nick Baker

With spring quickly approaching, many farmers are getting the itch to start field work, especially with each day longer and warmer than the last. As the planting window seems to get narrower each year and new planting technology advertised to increase the speed of seedling emergence it is important to remember monitoring soil temperature is critical for planting success and optimal yields. With increasing seed costs planting at an ideal temperature will be the first step to ensuring a healthy crop at harvest time. 

Soil temperature is key factor in deciding when to plant

Often times farmers look at the thermometer on the farmyard pole as an indicator of when they should plant, but it is important to remember that a warm spring day doesn't mean the soil temperature will match.  When checking soil temperature, be sure to measure the temperature at the level you are planting.  If you plan to plant corn at 2 ½ inches measure the soil temperature at the depth. The minimum soil temperature for planting corn is 50 degrees Fahrenheit, with optimal soil temperature being 55 degrees or warmer.  When planting at lower temperatures root and shoot growth are negatively affected leading to slow germination, uneven growth and development, a greater potential of late frost damage, decreased final stand counts, and lower yield potential.  Another risk of early planting specifically in northern areas are extreme temperature drops leading to refreezing of soil killing developing seeds.

Likewise for soybeans, planting at an ideal soil temperature will help with faster emergence, a more uniform stand, and even growth across the field.  The minimum soil temperature for planting soybeans is 59 degrees Fahrenheit, with higher soil temperatures equaling faster more uniform germination. Soil temperature during the first 24 hours after planting soybeans is crucial for seedling growth. Temperatures dropping below the recommended minimum during the first 24 hours after planting have shown in duplicated university studies to greatly reduce germination and final stand counts.

 The effects of planting into cold soil temperatures begin before the plant germinates.  Once planted, a seed will absorb up to 30% of its weight in water prior to germination occurring.  If the soil temperature is below the minimum recommended for planting the cold moisture will disrupt the cells reorganization and create a loss of seedling vigor or even death of the seed.  Even if the seeds do germinate, the seedlings can be weaker and slower growing. Further risks from early planting include frost damage leading to a decrease in yield potential or in the worst case scenario complete freezing and death of emergent plants. 


Other advantages to planting corn and soybeans into soils of optimal temperatures are a greater percentage of seeds germinating and surviving, which means even at lower planting populations we can see ideal stand counts which will save you money in seed savings. We can also see an advantage in starter fertilizer utilization in corn, the longer the seed sits in the ground and doesn't grow the greater the chance your expensive starter fertilizer will be leached from the root zone by spring rains. By planting into warmer soils you will notice faster germination and healthier root and shoot growth, which puts the roots into the starter band sooner promoting healthier plant development. 

When thinking about planting, remember the importance of monitoring soil temperature to ensure your crop the best opportunity for growth and yield potential don't just rely on the calendar.  Establishing corn and soybeans is an expensive endeavor. By following the best practice procedures for planting you do your part to ensure a successful crop. Just because your neighbor is planting doesn't mean it is a good idea for you to plant as well. Every farm is different.  Remember planting corn and soybeans shouldn't be a race, careful consideration of planting conditions and soil temperatures will help ensure a healthy start to your crop and hopefully higher yields come fall.           

Baker is the Rock County Extension agriculture agent.

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