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Soil friability is the key

Input of organic matter, reduced traffic, and tillage are all very important for making agricultural soil easy to work with.

[Translate to English:] Ved at behandle jorden godt kan den bevare en god smuldreevne. Foto: Henning Thomsen

The foundation for successful germination and high yields is created during the preparatory tillage and seeding operations. Here it is of particular importance that the soil is easy to work with – in other words, that it has a good crumbly structure. Senior scientist Lars J. Munkholm from Aarhus University will be explaining how farmers can nurse the soil to obtain the right texture at the 2014 Crop Congress to be held in Herning on 15-16 January.


- A friable soil is characterised by the larger clods fragmenting easily and by smaller soil aggregates being harder to break. Particularly fine textured soils can have problems with the soil becoming either too cloddy or too finely fragmented during soil preparation. The more friable the soil, the easier it is to make a good seedbed with the minimum use of energy, explains Lars J. Munkholm.


Water content is important

A poor friability occurs when the soil is either too wet or too dry. There is a "window of opportunity" in water content – the  window in water content for tillage – when the soil has a suitable friability. The drier the soil, the harder it also becomes and the more difficult it will be to break up the large clods. On the other hand, if it gets too wet, the large clods become sticky and plastic and will deform rather than break. The larger the difference between the dry and wet threshold, the better.


- In practice, a wide window in water content for tillage equals having plenty of time to prepare a good seedbed. With a wide window it will be easier to find opportune moments for seedbed preparation, when the weather is either to the wet side or to the dry side, says Lars J. Munkholm.


Friability depends on soil type. Generally, the higher the clay content, the harder the soil will get when it dries up. It will also more easily become plastic when it gets wet. Other factors also play a major role.


Organic matter matters

Many studies have shown that friability increases with increasing organic matter content. This means that less energy is needed for tilling. A few studies have also shown that the window in water content for tillage widens with increasing organic matter content.


The pool of organic matter in the soil is built up over decades and centuries, and it usually takes several years before the impact of changes in cultivation practices can be measured in the soil organic matter content. Recent studies have shown that an increased supply of organic matter may improve the friability of the soil after only a few years.


- It is not just the amount of organic matter that matters, but also very much the input of organic matter that affects friability. A continuous and adequate input of organic matter to the soil is a prerequisite for maintaining or improving soil friability, stresses Lars J. Munkholm.


Traffic and intensive tillage

Driving on wet soil cause compaction whereby large clods are formed. These  can be difficult to break when the soil dries out. A rotary tiller can usually cope with the problem. But it can also create new problems if the intensity is too high and the soil too finely fragmented. In this instance it has a propensity to puddle and hence form a crust.


With intensive soil operations in wet conditions there is a risk that clods are simply deformed rather than fragmented. This produces compact clods that can cause a problem for germination and which roots may have difficulties in penetrating.


Avoid the vicious cycle

Especially on low-carbon soils with limited annual inputs of organic matter (typically loamy soils in Eastern Denmark) there is a risk of getting into a vicious circle where the soil is only fit for cultivation within a short timeframe. Here there is a large risk of ending up driving on and cultivating the soil when it is too wet – in this way reducing its friability.


- You risk starting a vicious cycle with an ever increasing need for intensive tillage to provide a good seedbed. This trend can be countered by ensuring an adequate annual supply of organic matter combined with abstaining from driving and carrying out intensive tillage in wet conditions, explains Lars J. Munkholm.


Read also the article "The soil must be crumbly."


Read more about the 2014 Crop Congress here (in Danish).


For further information please contact: Senior scientist Lars J. Munkholm, Department of Agroecology, e-mail: lars.munkholm@agrsci.dk, telephone: +45 8715 7727, Mobile: +45 2515 2716