Tillage compaction from repeated discing may be only a few inches from the surface so plants are essentially restricted to only a few inches of topsoil. At the peak of the growing season the moisture in those few inches of topsoil just doesn't last long. In dry weather the effects of compaction really stand out. As harvest approaches keep in mind that heavy combines cause compaction. A wet fall can be worse than a wet spring in terms of causing localized areas of deep compaction.
Grain carts are among the heaviest equipment that ever enter the field.
It's best to keep grain carts and trucks out of the field if at all possible. If you have to come to the combine, confine compaction to a permanent traffic lane. Unload the combine frequently and set up all equipment on the same wheel spacing to minimize the compacted area. Repeated discing at the same depth may break the soil down into fine particles that make a good seed-bed, but pulverized soil is also easier to compact, especially when the soil is wet. The Water-Compaction Cycle Moisture in the soil acts like a lubricant allowing soil particles to move freely against each other.