In my previous post I mentioned pinch-row-compaction as a factor when considering whether to buy a center-fill planter, or a planter with an individual seed hopper on each row. I need to clarify some comments I made.
When I said that compaction between the center six rows on each pass of a planter could cause yield reductions of 20 to 30 bushels per acre within those six rows, it's important to note that the amount of yield reduction is dependent on soil type and moisture content of the soil. Not every pass with a big tractor pulling a center-fill planter will see major yield reductions in the center rows. If fields are dry, there may be minimal compaction and yields may fluctuate only slightly across the width of each planter pass.
But if soils are damp or easily compacted, it has been documented that yields in those center six rows can be reduced significantly because of damaged soil structure. The damage is due to reduced pore space that decrease oxygen availablity to roots, inability for moisture to move within the soil, and decreased root growth due to all those factors.
Don't blame center-fill planters alone for pinch-row compaction. Some tests indicate up to 80 percent of the damage is due to the tractor that pulls the planter. Center-fill planters just add to the existing problem.
If you don't believe that tractor weight/compaction is the main culprit for pinch-row compaction, just notice the yellow, stunted corn that's struggling to emerge in the wheel tracks left by tractors pulling field cultivators at an angle across wet soils this spring. It's impossible to document how much yield is lost in the diagonal wheel tracks left by tillage tractors, but if pinch-row compaction behind the planter cuts yields in wheel tracks by up to 30 bu/ac,, it only makes sense that field cultivator tracks do similar damage.
But in a late, wet spring, what other options do you have?