Farm Ireland
Independent.ie

Wednesday 24 May 2017

Careful cultivation the key to avoiding trouble

THE processes of wetting and drying, freezing, thawing, root growth, soil organisms and soil cultivations all contribute to the development of soil structure.

The wetting and drying cycle can affect the entire rooting depth. In heavier soils cracks open as the clay shrinks and roots can then grow through these cracks further loosening the soil.

In soils with low clay content, root growth is vital to maintaining an open structure. The exploring roots probe the soil and as they die, they leave channels for other roots to follow.

Fine crumb structures are developed in grassland by the fibrous roots of grasses. This can be seen when you shake out a tuft of grassland soil compared to a dug up section of bare soil.

Freezing and thawing also play an important role in developing soil structure by shattering clods in the surface layer. This process is vitally important in clay soils.

Earthworms and other soil organisms loosen the soil and provide drainage channels. They also produce binding agents which stabilise the overall structure.

Cultivation is required to produce a suitable rooting environment for crops, but cultivation can lead to compaction which is characterised by the lack of vertical cracks, making it difficult for the movement of roots and water. The larger pores are lost and this can lead to poor drainage.

Regular application of lime, farmyard manure and other organic materials are beneficial for both aggregation formation and stability since they promote the activity of soil fauna and soil micro organisms.

The structural stability of soil is also an important consideration. This refers to the soil's ability to resist being changed by wetting, cultivations or wheel pressure.

Soils with poor stability collapse when they soak up water i.e. they compact. Soils with fine sand or fine silt are particularly prone to compaction.

Soils with good structural stability are able to resist damage when wet, unless they are cultivated. Soils with a high clay content have better stability than those with low levels. Stability is also increased by the presence of lime and humus.



Structure

The ideal structure is one which encourages good water movement. A granular structure is very good as there is good space between the aggregates.

Structure is damaged when large and small particles separate out into layers causing air and water blockages. This is caused by working the soil when it is too wet, poaching land, overworking tillage land or compacting soil with heavy traffic.

The moisture of the soil is very important with regard to causing compaction. As soil moisture content increases the depth of compaction also increases. Close to 80pc of compaction from wheel traffic occurs in the first pass.

This causes patchy crop growth by capping, wheeling and preferential flow of water across surfaces (mini rivers in the field). When this occurs you may have to look at sub- soiling or deep cultivation. Often ploughing may be sufficient but you may have to go deeper to remove pans.

The problem with this is it can only be done in dry conditions. Sub-soiling in the wet can allow water to sit in the cracks over the winter and can make the soil even more prone to compaction.

It is important to stop unsustainable practices. Avoid bare ground as it is very prone to compaction.

Avoiding further damage from machinery is probably the most important consideration. Compaction recovery is slow as with the components that form structure in the first place. At least scuff the surface to remove linear harvesting lines. Allow recovery by putting the land into grass for a few seasons.

Sowing rooting crops will also help improve soil profile. Tap roots break down compacted layers deep in the soil profile e.g. mustard, rape. Fibrous roots break up layers near the surface e.g. grass.

In addition, soil organisms help aggregate formation and also burrow channels in the soil. On a positive note, the cycles of freezing and thawing as we saw in winter 2009 will also help to loosen the soil.

It would appear that some min-till land may require deeper cultivation down to 7-8 inches to correct problems that have arisen and also to provide a favourable environment for plant development. But if we have to cultivate deeper every year, it is the same then as ploughing but with the grass weed control problems.

Irish Independent