Ever heavier agricultural machinery puts soils under pressure


The wheel loads of agricultural vehicles have steadily increased since the 1960s. This puts soils under increasing pressure, resulting in soil compaction leading to poorer growing conditions for plant roots. At the same time, the water storage capacity of soils is decreasing, generating substantial costs to society. These are the findings of a study with Agroscope participation that was recently published in Soil and Tillage Research.

Increasing mechanisation in agriculture has two sides: on the one hand, it makes many field jobs easier for farmers. On the other hand, more power and performance also mean larger and heavier agricultural vehicles.

Compaction of soils increases – soil water storage capacity decreases

Researchers from Switzerland, Germany and Sweden used historical data on the weights of combine harvesters and tractors over the last 70 years to simulate how the weight increase has impacted mechanical stress levels in the soil and to predict the consequences for soil functioning. For example, wheel loads of combine harvesters have increased more than fivefold in the last 60 years, and modern agricultural vehicles may exceed wheel loads of 10 tonnes. This literally puts soils under pressure.

The simulations show a clear decrease in porosity of arable soil due to the increasing wheel loads of agricultural vehicles. As a result, the mechanical resistance that roots must overcome in order to grow in the soil has increased. As a consequence, root growth is restricted and it takes roots longer to access a certain volume of soil and reach nutrients and water.

The researchers see a link between this and the stagnation in crop yields observed in many European countries since the 1990s.

The increase in soil compaction has also reduced the hydraulic conductivity and water storage capacity of soils. The result is that less water can infiltrate into the soil, leading to more surface runoff. The researchers speculate that this has contributed to the increase in the incidence and severity of flood events.

High costs due to soil compaction

Although the damage caused by soil compaction is difficult to quantify in monetary terms, the researchers’ estimates show that the costs of soil compaction to society are substantial. The costs stem primarily from crop yield losses and flood damage, but also from increased greenhouse gas emissions and declining groundwater quality.

Taking Sweden as an example, the researchers estimated the compaction costs due to productivity losses and flooding damage at several hundred million euros per year.

As the wheel loads and total weights of agricultural machinery continue to increase, the risk of soil compaction is also likely to increase further – as are the associated damage and costs. In addition, the consequences of soil compaction are likely to become more serious with climate change: on the one hand, root growth in compacted soils is even more strongly affected during dry periods, which could further exacerbate crop yield losses. On the other hand, more intensive precipitation events will become more frequent, which could further increase the risk of surface water runoff on compacted soils – and thus the risk of erosion events and flooding.

The study shows that the mechanical stresses in soil caused by modern agricultural vehicles often exceed the strength of soil, so the risk of soil compaction is high. The study therefore proposes a paradigm shift: away from the trend towards ever larger and heavier vehicles towards lighter field machinery.