Wet Fall + Compaction = Next Year's Roots?

Ruts, packed headlands and infield compaction - you know we have it all this year. Wet soils, overcast, poor drying days and a late harvest have combined to make compaction and rutted fields a real problem. A little bit of tillage can put it out of sight and out of mind for now. Will we pay for this next year? Probably - it really depends upon the growing season. In the end it all comes down to roots and access to water.

Compaction research has shown yield impacts of 0 to 80 per cent depending upon growing conditions and the degree of compaction. So why the big range? Of course weather plays a part; generally if we have timely rains that keep the soil softer for roots to explore and rains that regularly feed the crop - compaction is not a big problem. Unfortunately those timely rains are rare. So what is really happening with the roots? Research from Northern Europe suggests that root response to soil compaction depends on the presence and distribution patterns of soil pores. We know that compaction decreases overall pore size and number. The common response of roots is to decrease overall root length - so less access to pores. There tends to be more horizontal root growth which concentrates roots in the upper layers of soil - again fewer pores to access water from. Roots also tend to respond to compaction by getter thicker. This costs the plant more in energy which helps to explain the yield hit but it also restricts the pore size that those roots can access. In summary, compacted roots are shorter and fatter and can't reach the water in pores.

Compacted layers can develop over time or after a wet harvest like 2014 and interfere with root development.

Figure 1: Compacted layers can develop over time or after a wet harvest like 2014 and interfere with root development.

What can I do to fix that?

In the short term there is not much that can be done to "fix" the problem. Many people are plowing or discing rutted fields in order to break up or at least cover the ruts. The damage to the soil profile is still there. Allowing more water and potentially frost in will help to start the recovery from compaction. Shallow tillage in the spring may help to create some short term pores for a part of the season.

Ruts and headland compaction can really reduce soil pores and in turn reduce water and air movement.

Figure 2: Ruts and headland compaction can really reduce soil pores and in turn reduce water and air movement.

If you still have harvest to complete - reduce the weight in harvest aids like grain buggies, load trucks outside the field (but don't leave muddy, unsafe roads) and if necessary concentrate compaction in travel lanes. These compacted zones can be dealt with later rather than compacting most of the field.

Surface soil compaction can occur easily in the spring, particularly after a wet harvest. This field seemed to show every spring equipment pass.

Figure 3: Surface soil compaction can occur easily in the spring, particularly after a wet harvest. This field seemed to show every spring equipment pass.

Longer term

Consider all the ways that you can build a stronger more flexible soil that can bounce back from bad harvest conditions. A varied or complex crop rotation with wheat, the addition of manure or other organic materials, use of cover crops and of course reducing tillage and overall traffic will help to build a more stable soil structure. Improving drainage can help to improve overall soil structure over time. Consider equipment weight and tire pressure to reduce ground pressure and the potential for deep and lasting compaction.


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