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Compaction has become a problem in recent years due to an increase of field equipment size and weight. Continuous corn has the potential to be more prone to challenges with soil compaction due to generally receiving more tillage and traffic than rotated ground. In addition, continuous corn acres may retain soil moisture longer than rotated ground due to higher amounts of residue. Compaction can have a negative effect on corn growth and development and may ultimately reduce the yield potential.
The main causes of soil compaction are field traffic and machinery. As the size of farms has increased, the size of equipment has also increased. Soil compaction is most likely to occur when soil moisture is at or near field capacity; when soil pores or voids are filled with equal parts of air and water. Water in the soil acts as a lubricant between the soil aggregates, allowing them to become tightly packed together.
Figure 1. Effect of soil compaction on corn root growth.
Excessive root compaction prevents root growth and limits root expansion (Figure 1). This can decrease water and nutrient uptake, causing drought stress and nutrient deficiency, most commonly, nitrogen (N), and potassium (K). Restricted root growth can also increase lodging later in the growing season. In favorable years, moisture availability, timing of rainfall, and fertilizer use can mask the effects of compaction. But the effect on yield potential has been reported to be as much as 10 to 20 percent in unfavorable years.1
To determine if soil compaction is a concern in your field, begin by testing the soil resistance to penetration with a tile probe, spade, or penetrometer. Dry soils have significant strength even if they are not compacted, so it may be beneficial to compare your observations and measurements with adjacent areas that may not be as compacted such as fence rows and adjacent idle lands. Compare different areas in your field at the same time to ensure similar moisture conditions. During the growing season, dig up plants and check for adequate root structure.
The first step to minimizing soil compaction is to avoid field work when soil moisture is at or near field capacity. It is best to let the field dry. Before starting any field cultivation, soil moisture can be checked with a simple field test. Mold soil from the 3 to 6 inch depth into a ball and drop it on a hard surface. If the ball does not break or crack, it means the soil is too moist for field work.
Secondly, try to drive loaded grain carts over tracks already present in the field. The most damage is done with the first pass of an implement. Controlling traffic patterns by using the same wheel tracks can help minimize the amount of land traveled. Wheel size and pressure should also be checked. Larger wheels and tires can allow better floatation and lower tire pressure can help reduce the load on the soil. You can increase the tire’s “footprint" with larger wheel diameter. A study at Iowa State University showed that using equipment with 6 pounds per square inch (psi) of surface pressure yielded 9 bushels per acre more than that of equipment with 16 psi of surface pressure.
Finally, conservation tillage practices are likely the best long-term solution. By avoiding tillage and passes through the field, there is less disruption of the soil structure. The additional crop residue can also help intercept raindrops and prevent surface sealing and compaction. Regardless of the tillage system, the essential question should be, “Is this trip really necessary?"
Compaction is an issue on many farms but it can be addressed through better management. Field operations should be avoided on wet soils and the benefits of conservation tillage should be considered.
1 Al-Kaisi, M., and Licht, M. 2005. Soil moisture conditions – considerations for soil compaction. Iowa State Integrated Crop Management. IC494, http://www.ipm.iastate.edu 2 Hanna, M., and Al-Kaisi, M. 2002. Understanding and managing soil compaction. Iowa State University Extension. PM 1901b. 3 Kok, H., Taylor, R.K., Lamond, R.E., and Kessen, S. 1996. Soil Compaction: Problems and Solutions. Kansas State University Extension. MS 7-96-5M. 4 Wortmann, C.S. and Jasa, P.J.. 2009. Management to minimize and reduce soil compaction. University of Nebraska –Lincoln. http://www.ianrpubs.unl.edu 5 DeJong-Hughes, J. Moncrief,J.F., Voorhees, W.B., and Swan, J.B. 2001. Soil compaction: causes, effects, and control. University of Minnesota Extension, FO-03115. Web sources verified 6/1/15