Managing wet weather soils
Autumn is a time to assess soil condition, according to grassland consultant, Dr George Fisher. He asks how your soils have coped with some wet summer months and suggests remedial action which will improve crop performance next year.
July 2023 was the sixth wettest on record for the UK and the wettest July ever recorded for Lancashire and Merseyside. The weight of water can cause capping on the soil surface, and harvesting in wet conditions compacts soils lower down. Soil compaction reduces soil health and crop yields, so what can we do to put things right ahead of next season?
Rain is heavy!
The 230mm of rain that Lancashire got in July represents 230kg falling on the soil. Whilst obviously not in one go, the sheer amount and force of rainfall can lead to surface compaction, which means that air can’t get down into the soil. And that’s important as aerated, aerobic soils have a healthier microbial population to turnover and provide nutrients for our crops. Anaerobic soil conditions caused by capping will reduce yields and lead to surface run-off, both of which are costly to farm finances and the environment.
A difficult wet harvest
The 2023 harvest season has been like dipping in and out of a leaking gazebo at a family barbecue as the rain rolls in and the opportunity to step outside with a beer is short and squishy underfoot!
It is easy to damage soils at harvest with traffic wheelings and pressure on time to get jobs done; it’s often the case that harvest happens when fields are a touch too wet – especially in wet seasons like 2023.
the dangers here are
- Loss of grass and crop yield and quality from soil compaction.
- Compaction reduces the success of autumn and spring-sown crops, particularly those that are min-tilled and directly drilled.
- Reduced water infiltration due to surface compaction that leads to waterlogging.
- Run-off from soils that are surface compacted, leads to loss of soil and nutrients.
Correcting soil compaction
Autumn is a good time to assess soil compaction and do something about it.
Knowledge and action at this stage can improve grazing and sowing windows and set soils up for optimum grass and crop growth next year:
- Dig soil inspection pits to assess where compaction is.
- Use spike aeration to alleviate surface compaction. This won’t have an immediate effect on plant growth but will allow air into capped soils.
- On harvested maize fields that don’t have an undersown cover crop, consider using minimal surface tillage or harrowing to break up soil and allow water to pass through the soil – this will avoid waterlogging and run-off over winter.
- Consider sowing a grass cover crop into fields that will not be sown until next spring; this will help avoid waterlogging and run-off and will provide forage for late autumn/early spring utilisation.
- If you are going to plough, make sure the plough is set to operate below soil compaction lower down the topsoil or subsoil profile, so the compaction is eliminated in the process.
- For compaction lower down the topsoil on fields that will not be ploughed, consider using a sward lifter or subsoiler to get rid of the compaction before winter sets in.
Using a sward lifter/subsoiler
The improvements resulting from effective treatment by sward lifting/subsoiling should be seen in a matter of weeks and months, with improved plant growth, better soil drainage and ground conditions for a longer grazing season. They can be used in an existing sward, although there will be some sward and soil surface disturbance, or when cultivating as part of the sowing process.
when using a subsoiler it is important to note that:
- The critical depth of the subsoiler is important and the working depth must be 2.5cm below the compacted layer. Subsoiling below the critical depth can result in more compaction because of the sideways resistance of the surrounding soil and will require more power to drive the machine, increasing costs.
- As a rule of thumb, the critical depth is approximately six times the individual loosening tines’ width, so a tine foot that is 8cm wide will have a critical depth of 48cm.
- If you subsoil when the soil is so wet that it is plastic (sticky), you will end up with a square mole channel and no heave in the soil.
- If you are unsure about the critical depth, or ar inexperienced in the operation, it is also wise to dig pits during the process to make sure it’s going to plan.
- It’s worth considering only subsoiling problem areas in a field, for example where compaction is resulting in standing water after heavy rain and around gateways, feeders and water troughs.
- Carrying out these remedies when the soil is too dry may cause ripping of the soil. And don’t subsoil an existing grass sward in spring as the heave and rip can reduce grass growth by around 10% in the four weeks after the operation, as the plant roots recover.
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