improving soil structure

All compaction is not the same. The same operation or grazing regime will not always give the same type of compaction.

To help improve soil structure effectively you need to know details of the nature and depth of compaction.  Use the GRASS visual soil assessment method

Once you have a good understanding of the pattern of any compaction in the field you can plan your own site-specific approach to healthy grassland soils.

  • Concentrate on problem areas of the field.
  • Use methods appropriate to the type of compaction.

Compaction type

Remedies to consider

Surface capping

(0–10cm deep)

 

  • Harrow
  • Soil aerator with spikes or knives
  • Add lime, if soil acid, or introduce organic matter to encourage earthworm activity
  • Establish deep rooting species – e.g. lucerne, chicory

Machinery

(10–15cm deep)

 

  • Subsoiler or sward lifter
  • Soil aerator with spikes or knives (but check depth carefully)
  • Plough

Plough pans

(>15cm deep)

  • Subsoiler or sward lifter
  • Deeper plough (below pan)
  • Mole plough (heavy soils only)

 

Whatever approach you take, you should always examine the effect of any in-field operation after a trial run, adjusting the equipment or stopping the operation, if necessary.

 

 

Sward lifting

If you are considering sward lifting, then apply the following guidelines:

1. Do not use sward lifters unless there are clear signs of soil compaction and the moisture content is suitable:

  • Examine the soil by digging holes to find out the nature and depth of any compacted layers, as well as the moisture content and friability of the soil
  • Sward lifting in conditions which are too wet will potentially lead to increased soil damage through smearing and wheel slip
  • Sward lifting in dry conditions is likely to lead to the formation of large clods, sward tearing and excessive surface heave giving an uneven surface finish

2. Sward lifting is not recommended in poorly drained soils if there is no drainage system present, as this is likely to cause excessive wetness in low lying areas which will potentially be at further risk of poaching and re-compaction. In these situations, and on heavy textured soils, a mole plough may be more effective in improving the soil drainage status than topsoil loosening

3. Sward lifting should be carried out in the autumn when grass growth is declining. If carried out in the spring or summer when grass is growing rapidly, disturbance to the root system can lead to severe sward death

4. Use the appropriate equipment and set it up correctly. The depth of compaction will dictate the depth of working required. Make sure the compacted layer is about 2.5 cm above the critical working depth of the implement used and the legs of the sward lifter should be 1.5 times wider than the working depth. Always, examine the extent of shatter on a trial run, adjusting the equipment or stopping the operation, if necessary.

5. Recently loosened soil is very sensitive to re-compaction and it is important to allow the newly loosened structure to be stabilised by root activity and natural soil processes:

  • Cut or graze the site immediately before treatment to ensure sward height is low (<4 cm)
  • Avoid grazing after loosening and conserve rather than graze in the first spring after treatment
  • If late growth needs utilising, use sheep rather than cattle to minimise re-compaction damage
  • Do not spread slurry on recently loosened fields

Adapted from ADAS Technical Briefing notes (ADAS, 1984; 1987).