The risk of compacting soil is always present but becomes greater during wet field conditions.
During a conference sponsored by the Washington County Land and Water Conservation Department together with University of Wisconsin-Extension, Francisco Arriaga, Extension soil specialist, reviewed ideas for detecting soil compaction and then offered management strategies to help minimize the impact.
Soil compaction reduces the amount of pore spaces in the soil which, in turn, reduces aeration and water retention.
"Compaction impairs root growth and development," he said. "It causes runoff, and water tends to accumulate in wheel tracks where it sets up conditions for soil erosion. That water is not available to plants.
"If less water is available to the plant, nutrient uptake is also limited, and nitrogen is denitrified and lost because of less aeration in the soil."
Arriaga outlined the causes of soil compaction including traffic on fields at the wrong time. Other causes include heavier equipment, high tire pressure, repeated traffic, excessive tillage and poor soil structure.
Tracks are an option for spreading out the weight of the equipment, but he said they also have some issues. Adding axels to grain carts and a good setup with duals on tractors with proper tire pressure can be just as effective or better than tracks.
"While duals put less pressure on the track, they still leave two tracks rather than one," he said. "Highway tires are the worst thing for fields."
With spring coming, he cautioned farmers to stay off their fields until they are dry enough.
"After doing any kind of tillage it's a good idea to wait and let those aggregates get together again before re-entering the field," he added. "Once you have compaction, it hangs around a long time."
Arriaga said many grain farmers are establishing permanent tracks in fields with help from GPS systems, and he cited the results of some studies that look at the benefits of this practice.
In the first example, traffic patterns were established for 30-inch rows with the planter spacing set at 60 inches and the combine head set at 120 inches. That left eight traffic lanes per 12 rows and resulted in 44 percent of the field driven over.
In the second example, an 8-row planter was used with 120-inch spacing and the combine also had 120-inch spacing. That resulted in three traffic lanes per 12 rows or 17 percent of the field driven over.
In a third example, he had a 12-row planter spaced at 60 inches between tires and 120 inches between tires on the 12-row combine. That resulted in 4 traffic lanes per 12 rows or 22 percent of the field driven over.
"Bigger isn't necessarily better," Arriaga said. "Bigger in these example was better than the first illustration, but the 12 row was not better than the 8 row."
The best way to determine if compaction is an issue is to examine the corn roots. A flat root is an indication of compaction. If roots go straight down and deep, there is no compaction issue.
Using a penetrometer is another way to check for compaction. Results of the reading are affected by clay content in the soil, soil moisture and bulk density.
Arriaga pointed out that sub-soiling is expensive and takes a lot of power.
"Set the sub-soiler about two inches deeper than the bottom of the compacted layer," he said. "Going lower will not be beneficial; it is expensive and could do more harm than good."
He reminded growers that sub-soiling when it is not needed, or going deeper than necessary, can actually decrease crop yields because it brings up soil that has no fertility in it.
Arriaga also sees some promise in using plants to break the compaction layer. Bio-tillage, as it is called, is done with deep-rooted cover crops that decay and also help build organic matter in the soil.
Freezing and thawing helps break up shallow compaction but does little for deeper compaction layers.
As farmers look forward to getting out onto the fields in spring, Arriaga suggested, "If you know you have a compaction issue, and the spring is wet, I'd hold off on trying to fix it until fall. If you do it when it is wet, as it could be this spring, it could do more harm than good."