Compaction is often thought of as a spring problem. However, in seven of the past 10 years, parts of Minnesota have had wet soil conditions during harvest.
What should a producer do when the soil is wet and harvest needs to be completed? Should producers risk significant compaction and harvest the crop or just stay off of the field? The answer is easy: harvest the crop.
Minimizing compaction under wet conditions
There are three major ways to minimize the extent of compaction at harvest. These include managing axle loads, properly inflating field equipment tires, and controlling field traffic.
Manage axle loads
Heavy axle loads and wet soil conditions will increase the depth of compaction in the soil profile. As loads increase beyond 10 tons per axle, the potential to compact the soil past the tillage layer also increases. Large 500 hp tractors, full combines, slurry tankers and grain carts can weigh between 18 and 40 tons per axle and whether equipped with tracks or tires, can create compaction down to 2 to 3 feet. Tracks and duals have better flotation than single tires. If combines or grain carts can be equipped with either of these choices, flotation would increase and allow the combine a few extra passes before getting stuck.
To minimize compaction due to the weight of the combine, combines should be unloaded on the headlands or unloaded more frequently.
Properly inflate tires
Before using any equipment in the field, it is important to check tire pressure. Not only does the proper inflation help reduce soil compaction, it also improves tractor efficiency. Studies have shown that given the same axle load, tire inflation (psi) will determine the depth and severity of compaction. Producers should check with their tire manufacturer or search the web for proper tire size and inflation rate for the carrying capacity of their equipment.
The theory behind controlled traffic is that 80 percent of the compaction occurs on the first pass through the field. Producers can use this to their advantage. While it may take awhile to replace equipment that will use the same wheel tracks, there is one piece of equipment that should receive special attention: the grain cart. The grain cart has the greatest potential to compact the soil due its large carrying capacity (>1,500 bushels) and a single axle on which to carry that weight.
Follow these tips when using a grain cart to minimize compaction:
- Try to use the same paths across the field.
- Use the combine's previous wheel tracks when unloading the combine.
- After loading the grain cart, follow those tracks down the field and take the headlands back to the semi or field entrance.
- Never diagonally cross the field. This will create multiple wheel track patterns at 80 percent compaction.
- If semis cannot be parked on the adjoining road, they should be kept on the headlands. Semis and gravity wagons may have a lower axle load, but the tire inflation is quite high.
Managing ruts after harvest
Inevitably, fall harvest will leave some ruts in the field. How should these be managed? First, wait as long as possible to start tillage operations, so the soil can dry out as much as possible.
Second, consider tillage depth. Tilling as deep as possible to shatter smeared soil or compacted layers may seem like a logical approach. However, deeper tillage and more aggressive operations are likely to damage soil structure, ultimately leaving soil susceptible to further compaction. The soil's best natural defense against soil compaction is good soil structure.
What tillage depth is recommended for managing ruts? On sandier soils, tillage should be 6 to 8 inches deep to fill in the ruts. On heavier soils, tillage should be as shallow as possible. Even with the best management, U of M research has shown that yield losses can occur up to 3 years after ruts were created.
Soil is one of the most important factors for growing a healthy crop. Preventing soil compaction or decreasing the affected depth will enhance water infiltration and storage capacity, timeliness of field operations while decreasing plant root stress and disease potential.
For more detailed discussions on soil compaction, see Compaction: Causes, effects and control and Tires, traction, and compaction.