Back to Basics.
There are only two items that control yield within commercially grown crops.
1) Light
2) Moisture.
You can of course expand upon that statement, but fundamentally too much or too little of these two factors influences crop yield every time.
Moisture.
Deep tillage (subsoiling) can be beneficial in alleviating soil compaction. This allows plant roots to explore more soil and access more moisture when they need it most (like during a dry spring or summer.)
Subsoiling is a practice that breaks up soil, usually 300 – 500 mm deep, to allow increased water movement and better aeration around the roots.
By comparison, conventional tillage breaks up the soil 300 – 400 mm below the surface, and in “areas of compaction,” such a practice is not sufficient for the next crop.
In some situations, soils develop “plough pans,” a layer of tight soil that acts like a plastic sheet preventing water from getting down to the roots below that 300 mm of soil. It can also be shown that some systems of minimum cultivation or direct drilling do the same thing except the “pan” exists 100 – 200 mm below the surface.
Seed is planted, it rains and the surface of the soil becomes saturated where-as below that pan it's “dry.” Consequently roots grow sideways and as the soil above dries roots cease to function effectively.
So how much is compaction of soil costing the farm business? Based on published research over a 10 year period on a silty clay loam, compaction causes a loss in yield of 12%.
Financially…
10 t/ha crop of wheat
12% = 1.2 t
1 t of wheat is worth? £150.00 (or should that be £250.00)
1.2 t = £180.00 /ha
If we halve this figure, since surely only half the field will benefit?
Therefore a 6% yield penalty is only costing us £90.00 /ha
Contractor charge for Subsoiling? £75 – 100.00 / ha