Integrated Agronomics: Compaction

By Mark S. Johnson, Extension Field Agronomist, Iowa State University Extension and Outreach

Each year, I am asked to look at fields where, it turns out, much of the problem is from compaction. Sometimes compaction was caused by machinery and never taken out and sometimes it was caused by the tillage itself. Either way compaction causes problems for roots by eliminating the macro pores.

By having only the smaller pores, water does not infiltrate as much and does not move down through the soil profile as easily. This in turn results in soil remaining water logged longer. Since the pores have a higher percentage of their space filled with water the roots simply cannot get enough oxygen. A good ratio for the pore space is to be 50% air and 50% water. Less than 50% air and roots “suffocate”. In addition, roots have a hard time penetrating this higher bulk density soil and, so between the two factors, they struggle.

I came across a comparison of older combines with newer combines. Read the piece here and think about the additional 26,567 lbs. in the empty combine and the additional 20,160 lbs. in the grain tank. There is even almost another ton of fuel in the newer combine. Think about how all that extra weight, 24.26 tons, is impacting soil structure each pass across the field. Then add in a grain cart holding anywhere from say 600 – 1500 bushels = 33,600 – 84,000 lbs. going across the field. Maybe emptying on each end when possible makes sense.

The same goes for tillage. For every action there is an equal and opposite reaction. For every pound of lift on a tooth, there is an equal pound of down pressure. That is one more reason one should do as little tillage as possible. Tillage destroys structure. So, tillage can affect you in two ways: 1) Breaking up beneficial structure and 2) Causing compaction at tip of point of the tool contact and below. That is when it is being done right. If the soil at the depth of tillage is too wet, it gets much worse. The compaction isn’t getting shattered and the condition is being compounded by the bottom and sides of the point smearing the soil.

2015 Series Schedule
Each year over 2,000 producers participate in a regional Crop Advantage meeting to hear updates on crop, pest and nutrient management, farm business topics, soil and water quality, and so much more.

Crop Advantage Series –  Held in or near our part of the state
DateLocationPre-register by
Jan 12AmesJan 5
Jan 14Storm LakeJan 6
Jan 20AtlanticJan 12
Jan 21Ft DodgeJan 13
Jan 22WaterlooJan 14
Jan 29CarrollJan 21

You can still register after that, even up to and including at the door. Early registration is $50, after that, $60.