Considerations for subsoiling this fall
Deep tillage can help alleviate soil compaction, but there are some things to consider before you start.
With the late summer and early fall weather as dry as it’s been around much of Michigan, soil moisture conditions may be ideal for using deep tillage implements to break up plow layers in early harvested fields. Most articles about deep tillage caution readers to stay out of fields when soil conditions are too wet to avoid creating a new pan layer, but there other things to consider.
Before moving ahead with deep tillage, determine if soil compaction is your problem. There are a couple of ways to do this. First, you can use a compaction probe or penetrometer, likely available at your local Michigan State University Extension or Conservation District office. Compaction layers that produce resistance over 350 pounds per square inch (PSI) are likely restricting root growth.
A second, more time-consuming yet likely more informative method is digging trenches to a depth of 2 feet, exposing a vertical soil profile. Look for roots that may be growing horizontally. Then, using a pocket knife, insert the blade with slow, constant pressure at various locations throughout the profile. Identify the location and depth of any compaction layers where you have a harder time pushing the blade through. Repeat either procedure at least four times throughout the field for each 50 acre piece. Realize that soil moisture status will influence penetration resistance.
The best time to do these sorts of assessments is when soils are wet to the point of field capacity, ironically the absolute wrong time to do deep tillage. Note that reduced-tillage fields may have higher bulk density and penetration resistance, but this does not necessarily mean root growth will be adversely affected. No-till soils often have more stable micro and macro pores too small or twisting for your penetrometer or knife, but perfect as channels for growing roots.
Also, consider the cost of deep tillage. MSU Extension’s “2017 Custom Machine and Work Rate Estimates” estimates the per acre cost of running V-rippers and subsoilers at a range of $14 to $35 per acre, with an average price of $20.23 per acre.
How much of an increase in yield would you need in a corn-soybean rotation to pay for the operation? Let’s use a value for corn of $3.50 and a $0.20 basis, and a value for soybeans of $9.50 and a $0.50 basis. Assuming subsoiling every other year, you would need to realize an increase in corn yield of 3.1 bushels per acre, and an increase in soybean yield of 1.1 bushels per acre. Is this achievable? Certainly, but plugging your own numbers in helps you be confident with your decision. Consider treating only the areas where compaction is the problem, like headlands and other heavily trafficked areas.
Finally, remember that treating compaction with a subsoiler is only a temporary fix if steps aren’t taken to avoid future compaction. These steps include:
- Reducing axle loads.
- Decreasing contact pressure (use wide flotation tires).
- Controlling and concentrating traffic patterns/travel less of the field.
- Avoiding operations when the field is wet.
- Minimizing tillage.
For in-depth reading on this topic, check out the sources I’ve consulted:
- Soil management and health - Compaction by University of Minnesota Extension
- Soil compaction not always grounds for deep tillage by Purdue University
- Does Deep Tillage Pay? By University of Illinois Extension
- Avoiding Soil Compaction by Pennsylvania State University Extension