How to assess soil structure to improve grassland quality
©Tim Scrivener Livestock farmers are being encouraged to take a look at their soil structure, after a study revealed fewer than half of grassland fields have good soil composition.
A Defra-funded study of 300 grassland fields found just 40% had good soil structure.
According to Liz Genever, AHDB Beef and Lamb livestock scientist, now is the time that farmers should be looking at the state of their soils and taking any necessary action.
See also: Get more soil management advice
“At the end of the summer, soils are less dry and it’s a good time to assess their structure,” she says.
Using aerators or sward lifters in the autumn means the soil and the roots have the winter to recover before the high demands of spring when grass growth really gets going.
Combating compaction
In cases of mild compaction, Dr Genever says soils do have a capacity to recover on their own, especially when the cause, such as grazing livestock, is removed.
In these situations she says it may be worth monitoring the field over a few weeks to see whether it improves. “Taking photos on a phone is a simple but useful way to track soil condition,” she adds.
Dr Genever suggests four quick steps to assessing soil structure
- Surface assessment – Look at sward quality to identify potentially damaged areas which require further assessment
- Soil extraction – Dig out one spade-sized block of soil (depth approximately 30cm). Cut down on three sides and then lever the block out, leaving one side undisturbed. Lay soil back on sheet or tray.
- Soil assessment – Gently open the soil block like a book to break it up
- If the structure is uniform – assess the block as a whole
- If there are two or more horizontal layers of differing structure identify the layer with the poorest structure
- Carry out the rest of the assessment on this limiting layer
- Soil scoring – Break up the soil with your hands into smaller structural units or aggregates (soil clumps)
- Assign a score by using the table below
- A score of 1 or 2 is good; a score of 3 moderate; and 4 or 5 is poor and requires management action
- Record depth of limiting layer to assess management options
How to score your soil
|
Soil structure score |
Structure description |
Action to take |
|
1 – Crumbly |
|
Reassess after equipment crosses the ground or grazing in wet condition or every two years. |
|
2 – Intact |
|
Reassess after equipment crosses the ground or grazing in wet condition or annually in spring |
|
3 – Firm |
|
Consider infrastructure changes (such as back-fencing, multiple filed entrances or tracks) to minimise traffic in marginal weather conditions |
|
4 – Compact |
|
Consider using sward lifter or aerator (if poor soil structure <10cm) or topsoiler or sward lifter (if poor soil structure deeper than 10cm). Assess sward, then plough and reseed if required |
|
5 – Very compact |
|
Use sward lifter or aerator (if poor soil structure <10cm) or topsoiler or sward lifter (if poor soil structure deeper than 10cm). Assess sward, then plough and reseed if required |
If soils score 4 or 5 on the scale then Dr Genever says action is required with an aerator or sward lifter.
“There is good evidence that using aerators or sward lifters in soils without poor structure has limited benefit and can cause damage, especially if the soil conditions are not appropriate.
If an aerator or sward lifter needs to be used, it is important to make sure soil moisture conditions are correct to avoid further damage,” she says.
“If a handful of soil obtained from the depth that needs to be worked gives a moist smooth surface when rolled then it is too wet to work. If the soil starts to crack then the soil conditions are appropriate.”
Aerators and sward lifters need to be working 2.5cm below the problem area. Dr Genever suggests digging holes to make sure the equipment is doing the correct job.