One study that caught my eye was the reported variability in yield across the width of very large planters. This study was done on farms in Minnesota using three planter configurations.
- 36 rows, 22 inch spacing, centre fill
- 36 rows, 20 inch spacing, centre fill
- 48 rows, 20 inch spacing, row unit boxes
Twelve locations were harvested and the average yield on the outside third of the planter was 11 bu/acre higher than the inside third. There was significant difference between the outside third and the middle third in 9 out of the 12 locations.
While there is not much a grower can do to change his planter configuration being aware of the compacting effect is useful knowledge. Keep in mind there is sometimes a trade off between timely planting and less than perfect soil conditions.
One last consideration is the row effect on hybrid evaluation. This is something I have been guilty of doing. As an example, I have taken a 12 row planter and split it into three 4 row plots. Splitting a planter into more than two equal halves could unfairly bias hybrid performance. The outside rows would have an automatic advantage.