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2/23/2009 - 3/1/2009

Not too Early to Think About Spring Moisture Conditions, Consideration for Soil Compaction

By Mahdi Al-Kaisi, Department of  Agronomy; Mark Hanna, Department of Agricultural and Biosystem Engineering; Mark Licht, Extension Field Agronomist

Normally early spring soil moisture is a challenge when the soil profile is fully charged. Depending on the amount of snow we receive and duration of winter, there is a tendency for producers to enter fields at less-than-ideal soil conditions, especially when there is a short window for conducting field operations.

Soil compaction caused by field traffic and machinery increases with high soil moisture. Over the past decade the size of Iowa farms has increased, leading to larger and heavier equipment. However, equipment size is only one factor among many causes of the soil compaction problem. Rushing to the field when the soil is wet, combined with the weight of equipment and traffic pattern in the field, can increase chances for severe soil compaction. Conducting field operations during wet field conditions compounds the amount of compaction occurring.

Maximum soil compaction occurs when soil moisture is at or near field capacity (Figure 1) because soil moisture works as a lubricant between soil particles under heavy pressure from field equipment.

soil compaction chart

Figure 1. Relationship between soil moisture and potential soil compaction.

Indications of soil compaction during and immediately following a normal rainfall include slow water infiltration, water ponding, high surface runoff, and soil erosion. Additionally, soil compaction can be diagnosed by stunted plant growth, poor root system development (Photo 1), and potential nutrient deficiencies (i.e., reduced potassium uptake). These soil compaction symptoms are a result of increased bulk densities that affect the ideal proportion of air and water in the soil.

              soil compaction

Photo 1. Effect of soil compaction on root growth at three different soil bulk densities: Low, 0.7 g/cm3; Medium, 1.1 g/cm3; High, 1.6 g/cm3.


The most efficient way to verify soil compaction is to use a tile probe, spade, or penetrometer to determine a relative soil density. Soil moisture conditions can have a significant effect on penetration resistance.

For example, in dry soil conditions soil penetration resistance is much higher than wet conditions because soil water acts as a lubricant for soil particles. Therefore, it is wise to determine soil compaction early in the season or compare observations and measurements from suspected areas with adjacent areas that have little chance of soil compaction due to traffic patterns.


Management decisions to minimize soil compaction
The most effective way to minimize soil compaction is to avoid field operations when soil moisture is at or near field capacity. Soil compaction will be less severe when soil tillage, fertilizer application and planting operations occur when the field is dry. Soil moisture can be determined using a hand ball test or observing a soil ribbon test.

Properly adjusted tire size and correct air pressure for the axle load being carried is a second management tool. Larger tires with lower air pressure allow for better flotation and reduce pressure on the soil surface. Additionally, using larger tires that are properly inflated increases the "footprint" on the soil.

A third management decision is to use the same wheel tracks to minimize the amount of land traveled across. Most damage occurs with the first pass of the implement. Using control traffic patterns can be done effectively by using implements that have matched wheel-tread configuration for soil preparation, planting, row cultivation, spraying and harvesting.

Soil compaction can be a serious problem for Iowa farmers, but with proper farm management, compaction can be minimized. Remember to hold off soil tillage operations until soil conditions are drier than field capacity and look into the benefits of conservation tillage systems.

Top 10 Reasons to Avoid Soil Compaction
1. Causes nutrient deficiencies
2. Reduces crop productivity
3. Restricts root development
4. Reduces soil aeration
5. Decreases soil available water
6. Reduces infiltration rate
7. Increases bulk density
8. Increases sediment and nutrient losses
9. Increases surface runoff
10. Damages soil structure


Source: Iowa State University Extension publication PM 1901b - Understanding and Managing Soil Compaction -- Resource Conservation Practices



Mahdi Al-Kaisi is an associate professor in agronomy with research and extension responsibilities in soil management and environmental soil science. Mark Hanna is an extension agricultural engineer in agricultural and biosystems engineering with responsibilities in field machinery. Mark Licht is an Iowa State University Extension field agronomist serving Calhoun, Carroll, Crawford, Greene, Ida, Monona, and Sac counties.

February 23 Crops and Weather Update

By Doug Coooper, Extension Communications Specialist

Iowa State University Extension climatologist Elwynn Taylor, integrated pest management specialist Rich Pope, and economist Robert Wisner take a look at the 2009 growing season during the Extension crop and weather weekly interview segment with Doug Cooper, Extension communication specialist.

Long term weather forecasts from the National Weather Service offer hope for at least a chance of decent weather during the 2009 growing season, according to Extension climatologist Elwynn Taylor. He says La Niña is still in place, but may disappear or weaken by April.

Rich Pope says spring planting and field work are not too far away. He reports that Iowa State University Extension specialists are gearing up for the new season.

Robert Wisner says ethanol plants are experiencing an economic crisis as corn prices and crude oil prices decline.

Consider Frost Seeding or Interseeding Pastures This Spring

By Stephen Barnhart, Department of Agronomy

Producers wanting to add to or improve forage in their existing pastures should consider using either the frost seeding method in February and early March, or interseeding in later spring months.
The frost seeding method involves spreading forage seed on existing pastures during the late winter or very early spring while the ground is still frozen. Freeze-thaw cycles, with help from early spring rains, then provide shallow coverage of the seed.
Frost seeding is the easiest method producers have to add new forage grasses or legumes to their pasture, and is likely the least expensive method.
To increase this method’s success, one should spread seed on the thinnest pasture sod areas first and on areas where bare soil has been exposed due to heavy grazing or disturbance.
One common misconception about frost seeding is that spreading the seed on top of snow works best. The goal of frost seeding is to get seed on bare soil.  This is more effectively and safely done without snow cover.
Red clover has been the forage species of choice in Iowa for frost seeding. Other legumes, such as white clover, birdsfoot trefoil and alfalfa also can be frost seeded but with less success than red clover. In general, frost seeding does not work as well with grasses.
Research has found that following a few steps will improve the success of frost seeding.  See Iowa State University Extension PM 856 - Improving Pasture by Frost Seeding for suggested seeding rates and guidelines. 
Interseeding offers an opportunity for improving pasture productivity too.  Interseeding involves using a no-till drill to aid in the incorporation of a legume or a more productive grass into an existing pasture sod. Interseeding is normally done from mid-March through early May, when soil moisture and temperature are more suitable for rapid seedling establishment.

Interseeding can be accomplished with relatively few field operations. Opening of the grass sod, shallow seed placement, and seed cover¬age are required. A number of drills are available that can be used in sod-seeding efforts. Some of these drills may have improved features related to sod penetration, depth control, seed metering, or coverage that improves their effectiveness in sod seeding situations. Equipment limitations for sod seeding implements sometimes are overcome by operator experience and home shop modifications.

Legumes interseeded into grass sod should increase pasture yield, improve forage quality, and eliminate or minimize need for nitrogen fertilizer. Clovers, alfalfa, birdsfoot trefoil have been successfully interseed. The more efficient seed placement provided by a no-till drill allows many of our more productive perennial forage grasses to also be successfully established by interseeding. Thin, low-producing, grass sod might best be improved by interseeding a grass legume mixture.

Delaying seeding into late spring to improve growing conditions will often lead to greater competition from the existing grass sod. Close grazing in the fall or spring, ahead of interseeding, will help reduce sod competition. Contact herbicides are sometimes also used to temporarily further reduce competition from plants present in the stand.

Interseeding success depends on paying attention to details, timeliness, careful management of sod completion, controlling seeding depth to no deeper than ¼ to ½ inch, and a little bit of luck with weather.

Interseeding research has been conducted in many parts of the U.S. and around the world. It shouldn’t come as a surprise that the conclusions from these efforts all point to several very important issues that must be met for successful interseedings. See Iowa State University Extension PM 1097- Interseeding and No-Till Pasture Renovation for more suggested seeding rates and guidelines.

For more information, contact Stephen K. Barnhart, Extension Forage Agronomist, Iowa State University, and Ames, Iowa. Phone  515-294-7835 or


Stephen K. Barnhart is a professor of agronomy with extension, teaching, and research responsibilities in forage production and management.

This article was published originally on 3/2/2009 The information contained within the article may or may not be up to date depending on when you are accessing the information.

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