Modern tillage farming practices make soils more vulnerable to the impact of heavy machinery and traffic volumes.
But, according to Teagasc, tillage land can still function well if handled with care.
Until the 1970s, virtually all tillage happened on mixed farms. Typically fields were in grass for seven to 10 years followed by three years annual crops, before returning to grass.
This resulted in resilient soils with high organic matter levels.
Today, as a result of specialisation, most tillage fields are cropped for 40 to 50 years. This leads to lower soil organic matter levels and greater vulnerability to soil structural damage.
However, soils can still function with low organic carbon levels, but they must be managed with great care.
Soil moisture
Soil moisture is the most critical factor. Very dry soils resist damage to their structure. But as they get wetter, soils become weaker and are more easily compacted. Machinery, or animal, traffic can cause compaction.
Within the soil profile, compaction is what happens when the aggregates are forced together – shrinking the empty pore spaces between them.
Even more serious structural damage occurs where the aggregates themselves are broken down.
So when is it safe to work on soil? This is not a straightforward question. Growers usually judge conditions by gauging how ‘sticky’ the soil is on a spade, a boot, or in the hand; with the soil’s texture (sand, silt and clay content) influencing the result.
Often, however, moisture in surface layers may not be a good indication of moisture levels down the profile. Heavy axles can have their greatest impact on wet soil layers well below the surface.
In autumn, the soil can be drier underneath. A plough and one-pass sowing system can often work well in these circumstances. As soils wet-up over the normal autumn sowing period, however, there are challenges for all tillage systems.
In spring after a wet period, the drying top soil can often mask wetter conditions below.
In this situation, which was common in 2024, it would be better to wait – but for how long? Most growers will work the ground when they gauge the tillage tools won’t damage the soil.
While this is good practice, we cannot ignore the further impact of machinery weight, through the tyres, both in the field, and particularly on headlands.
This type of soil damage must be prevented as remediation by further tillage e.g. sub-soiling, can leave the soil vulnerable to serious damage from subsequent traffic.
Reducing machinery ground pressure
The ground pressure exerted by a wheel can be reduced by decreasing the load or weight on the wheel, or by increasing the tyre size or contact area between the tyre and the ground.
Loads can be decreased by reducing machine size and this should be carefully considered when selecting machines.
We sometimes seem to be pursuing scale to reduce labour at all costs. This may not always make sense with our field sizes and distances between fields and land blocks.
While the manoeuvrability of mounted equipment is a benefit in smaller fields, the use of trailed equipment can greatly reduce axle loads.
Unfortunately, much of the trailed equipment available is not designed for manoeuvrability in small fields or trafficability in wetter conditions.
Crop choice
Finally, crop choice can also play a role. Oilseed rape for example is sown in August and harvested in July, ensuring that the main machinery operations are carried out when the soil is likely to have good carrying capacity.
Conversely, vegetable crops requiring excessively cultivated seedbeds, compounded by destoning, and with contract-determined harvesting dates (e.g., carrots), should only be considered on light textured soils on free-draining sites, with good field access, to reduce the risk of damage.