Seedbed Preparation

Field Facts by Jim Boersma, Pioneer Product Agronomist

Seedbed preparation sets the stage for optimal growth and development throughout the growing season and ultimately has a major impact on yield potential. This fact sheet reviews management decisions regarding when to begin seedbed preparation and how to minimize compaction.

Determining When Soils are Fit

The following soil test is a quick method to help gauge if soil is ready for spring tillage and seedbed preparation.

Take your trowel and dig down 2 to 4 inches into the seedbed. Grasp a handful of soil from the trowel and squeeze it. Soils are too wet for spring tillage if any of the following are true:

Does it feel tacky? Can you make a ball that sticks together? Does it form a ribbon when squeezed between your thumb and forefinger (as shown below)?

Soil should be dry enough in the top 4 inches that it cannot be formed into a ribbon with normal compression in your hand. Soils in proper condition for seedbed preparation should crumble between your fingers. Soils that crumble easily are ready for spring tillage operations, creating favorable tilth for early growth while minimizing soil compaction.

Soil too wet for field work.

Ribbon indicates soil is still too wet for field work.

If soil crumbles when pressed, soil is suitable for field work.

If soil crumbles when pressed, soil is suitable for field work.

Improving Seedbeds for Optimum Yield Potential

  • Evaluate every field for soil moisture conditions. Use the simple “ribbon” test to determine soil conditions and fitness for seedbed preparation.
  • Reduce compaction with proper tire inflation and counter weights for spring tillage and planting equipment.
  • Under dry conditions the use of a packer/roller may help improve seed-to-soil contact and germination.
  • Select hybrids with above average stress emergence scores for earliest planting dates.
  • Wait until soils reach a minimum of 50 degrees at the 2-inch depth prior to starting planting.

Soil moisture conditions can change between the time the seedbed is prepared and planting begins in the field. If soils become wet, be patient and allow them to dry out. Try to work fields as close to planting operations as possible. Planting into wetter soils, or working soils too wet will cause sidewall compaction from the disk openers. This type of compaction is frequently the cause of uneven emergence. In addition, this compacted soil creates a compaction barrier that corn and soybean root systems will have difficulty penetrating. This can reduce moisture and nutrient uptake and yield potential.

Wet soils at planting can lead to smearing of the seed furrow sidewall by the disk openers. This can lead to uneven emergence and restricted root growth.

Soil compaction restricting corn root growth.

Wet soils at planting can lead to a compaction barrier that restricts root growth and yield potential.

Proper Tire Pressure

Compaction in the top 6 to 8 inches is related to soil moisture conditions, inflation pressure (psi) and the total axle load of the equipment. One thing that can help prevent soil compaction is ensuring that your equipment has proper tire pressure and counter balance weight. Wet soils at planting can lead to smearing of the seed furrow sidewall by the disk openers. This can lead to uneven emergence and restricted root growth.

Uneven corn emergence due to wet soils at planting.

Wet soils at planting can lead to smearing of the seed furrow sidewall by the disk openers. This can lead to uneven emergence and restricted root growth.

Most new 4-wheel-drive tractors are equipped with radial tires that should be inflated to 8 to 10 psi. A properly inflated radial tire will have a wider base and will have a noticeable "cheek"; showing in comparison to older bias-belted tires, which were typically inflated to pressures of 20 to 25 psi. It is not uncommon for radial tires to be overinflated to 20 to 25 psi because of previous experience with older bias-belted tires and the fact that a grower may not be accustomed to the look of a properly inflated radial tire. Properly inflating tires will not only significantly improve the ride in the tractor and improve fuel efficiency and pulling power, but will also help prevent compaction. For example, a tractor equipped with 18.4 R42 tires carrying an axle weight of 3,200 lbs would have a footprint area of 272 sq. inches when properly inflated at 8 psi. However, the same tire with an identical axle load would have a footprint area of only 125 sq. inches when inflated to 24 psi. Proper tire inflation more than doubles the footprint of the tire, spreading the load of the tractor across a much larger surface, thereby reducing compaction.

Consider these tips when getting your tractor ready for spring operations:

  • Check tire pressure and inflate your tires based on the manufacturer's recommendations. Radial ply tires should be inflated to 8 to 10 psi.
  • Always check the inflation pressure early in the morning before you go to the field. For optimum performance check and maintain tire inflation pressures at least once every 2 weeks.
  • Use only low pressure gauges to check for inflation to obtain accurate readings.
  • Properly inflated (low pressure) radial ply tires will also help reduce power hop problems in most cases.
  • Remember that bias ply tires require higher inflation pressures than similarly-sized radial ply tires. Serious tire damage can occur from sidewall buckling if under-inflated.
  • Proper ballasting is necessary to obtain optimum performance from your tractor. The amount of ballast and the proper split in weight between the front and rear axle will depend on the type of tractor, the type of implement and soil conditions. Contact your dealer for specific information for your equipment.

Use of Packers to Firm Seedbeds

Adequate seed-to-soil contact is critical for proper germination and nutrient uptake. Under dry conditions, the use of a packer may help firm seedbeds and improve stand establishment. The use of packers under dry conditions has also been observed to aid root interception and uptake of nutrients such as zinc and potassium. However, the use of a packer in wetter conditions can increase bulk density of the soil and reduce soil tilth. The decision to use a packer should be made on a field-by-field basis as current conditions require.

Using packers to firm seedbeds.

In areas of Minnesota with severe iron deficiency chlorosis, some growers are experimenting with the use of rollers to firm seedbeds. This management technique is in response to the observation that iron chlorosis is often reduced or eliminated in wheel tracks. University of Minnesota Soil Extension Scientist George Rehm has reported significantly lower soil nitrate nitrogen levels in wheel track areas that are green compared to chlorotic areas of the same field. This may lower nitrate levels in legumes growing in the wheel tracks. It is speculated that higher nitrate levels in legumes can block the normal uptake of iron, resulting in chlorosis.

More research is needed to fully understand the impact of nitrate on iron deficiency chlorosis in soybeans and possible management strategies, including the use of packers. For the present, the best management strategy is to select a variety with adequate tolerance to the level of severity of iron deficiency chlorosis for your soil types.

Additional Information

Photos courtesy of Jim Boersma.