BU-07400     2000

To Order

WHAT'S NEXT

Do you have a compaction problem on your farm? Is it affecting your bottom line now, or will it in the future? You can begin to answer these questions by assessing your risk for compaction and monitoring your farm for compaction.

Assessing Compaction Risk

Use "Six Steps to Minimizing Compaction" on page 2 to analyze your operation. Here are some questions you might ask.

• Do you have enough time for field work in the spring? How many days does your field work require? Compare this to the number of days suitable for field work in the spring. (Your nearest University Research and Outreach Center may have historical data on the number of days suitable for field work.) You might learn that for 1 in 10 years the weather will not allow you enough days to finish field work by the latest profitable planting date. Maybe the ratio is 3 in 10 years, or 1 in 20 years. Are you comfortable with that ratio? If not, how might you change your operation so you feel less pressure to drive on wet fields?
• What is the axle weight of each of your pieces of equipment? Those over 10 tons pose a significant risk for subsoil compaction.
• When is the last time you evaluated your tractor tire pressure or the amount and location of ballast? Ask your Extension educator or equipment dealer for the latest advice on these.
• What would it take to establish a controlled traffic system or to increase soil organic matter levels?

Four Ways To Monitor Compaction

1. Use a soil probe

A penetrometer is a tool that measures soil strength when pushed into the soil. High readings can mean that soil is compacted or that it is dry, so consider the soil moisture level when interpreting readings.

With a bit of practice you can locate compaction problems without special equipment. Push a metal rod, stiff wire, or a fiber-glass fence pole into the ground using even pressure. Compare the feel of different parts of a field such as headlands, between rows, or in low spots. (Remember that wet soils are easier to push through.) Feel for changes in density as you push through the soil and note the depth of the compacted layer.

2. Watch for indicator weeds

Healthy stands of bindweed, quackgrass, mustards, velvetleaf (button weed), horse nettle, and pineapple weed are thought to indicate hardpans.

Compacted soil that is poorly drained and going acid will support sorrels, dock, horsetail, and lady’s thumb. Foxtail also likes compacted, poorly drained soils.

3. Study roots

Whenever you dig a hole, for any reason, look at the roots. Roots turn sharply when they run into a compacted area and are less common within dense layers.

Some people pull up a plant (a weed will do) and study the fine root hairs. Normally, they grow straight out, perpendicular to the root. If they grow out in other directions, it may indicate compaction.

4. Measure soil bulk density

Soil density is the weight of the soil divided by its volume. It is an indicator of compaction, but not always a good indicator of how plants will respond to the compaction. Soil texture is one explanation for this. High density in a sandy soil might not restrict root growth, while root growth in clay soils could be restricted at the same density.

Instructions for measuring bulk density are in the USDA Soil Quality Test Kit. Ask for it at your local Soil and Water Conservation District office, or on-line at: http://www.statlab.iastate.edu/survey/SQI/kit.shtml

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