Increased weight of farm machinery is a problem for the fertility of agricultural soils. The weight can lead to soil compaction, which may inhibit root development and reduce crop yields.

However, by using permanent lanes in the fields – also known as controlled traffic farming – in the production system of organic vegetables, the yield can be increased - but to what extent depends on both the soil type and the crop species.

This is the result of a study from the Department of Food Science, the Department of Mathematics and the Department of Engineering at Aarhus University, which has looked more closely at the effect of heavy vehicles in organic vegetable production.

In a field trial, they have tested the effect of two different traffic systems by tractors and agricultural machinery: random traffic farming (RTF) and controlled traffic farming (CTF) in permanent lanes that limits soil compaction to the lanes.

Soil type and crop species play an important role

Some soil types are exposed to more damage from agricultural machinery than others. Wet soil, in particular, is prone to damage, and especially clay soil has high water content.

In order to be able to compare the effect of soil type, the experiment took place on two organic farms in Denmark - one with coarse sand in the period 2013-15 and the other with fine sandy loam in the period 2013-16. Based on the Danish soil type classification, the experiment was carried out on JB no. 1 and 6.

In order to be able to compare the effect of crop species, both white cabbage, potatoes, beetroot and winter squash were examined. More specifically, the researchers investigated the impact of the two production systems on crop yield, root growth and nitrogen content under the conditions of the two types of management.

The results showed that there are advantages associated with controlled traffic farming, but that both the soil type and the crop species matter.

- We saw the most significant results on the farm, Skiftekær Økologi, which had fine sandy loam. The yield of white cabbage, potatoes and beetroot was, respectively, 27%, 70% and 42% higher (2015) and the yield of winter squash 43% higher (2016) when permanent lanes were used. White cabbage (2015) as well as potatoes, beetroot and winter squash (2016) had between 2 and 25 times more roots when permanent lanes were used, says Hanne Lakkenborg Kristensen, Associate Professor and leader of the Science Team Plant, Food & Sustainability at the Department of Food Science.

On the farm, Vostrup Øko, which had coarse sand, there were also some positive effects of controlled traffic farming. The researchers found, among other things, that the use of this traffic pattern resulted in 1.4 times more roots on the beetroot (2016).

The mineral nitrogen content and potential mineralization of nitrogen of the soil were either the same under the two traffic patterns - and in some cases higher when permanent lanes were used. This indicates that nitrogen availability was either maintained or increased by the implementation of controlled traffic farming - i.a. due to the increased plant growth and subsequent mineralization of plant residues.

Permanent lanes recommended

Overall, the results of the study indicate that controlled traffic farming, all other things being equal, can benefit organic farms.

- Our study shows that permanent lanes can maintain or improve both crop yields and nitrogen uptake - and that permanent lanes can contribute positively to root growth. We have not found any negative effects of using permanent lanes in organic farming, regardless of whether it is coarse sand or fine sandy loam - and regardless of which vegetables are involved, says Hanne Lakkenborg Kristensen and concludes:

- Based on our research, we would, therefore, recommend the use of controlled traffic farming in organic farms. In vegetable production, it requires that the cultivation beds are fixed and that all machines have the same track width. Technologies for precise control of tractors and machines in permanent lanes are optional equipment that, according to Statistics Denmark, has become more widespread on agricultural holdings in recent years.

Changed practice at Skiftekær Økologi

At Skiftekær Økologi, who participated in the study with fine sandy loam, the owner Peter Bay Knudsen says that they have taken the results into account:

- After the positive results that we had when participating in the study in 2013-16, we have used permanent lanes only in all fields. We are consistently used the system because we have experienced a positive impact on yield. In practice, we use permanent lanes and we manage the soil in depth without plowing. Instead, we harrow the soil.

Research facts