Why compaction is the key to good soil health

Aug 26, 2015 | ,

Peter Muller, Reef Catchments

Check to see if soil compaction is occurringSoil health is a hot topic and in Mackay the compaction in a sugarcane paddock was recently investigated as part of one of Reef Catchments sustainable agriculture projects.

One of the ways of checking to see if compaction is occurring is to dig a small pit, either by hand with a spade or by backhoe and to examine the soil structure.

Reef Catchments project officer, Peter Muller, said anyone could do this once they understood what to look for. He said it was also useful compare soil structure from an undisturbed site with that from a cropping or grazing paddock.

“There has been a lot of focus on the chemical and biological aspects of soil health such as microbiology, organic matter, and alternate farming systems,” Mr Muller said.

“However physical soil health, including soil structure and compaction is also essential. Plough pans and compacted layers can reduce root penetration and therefore yield.”

He said a highly compacted soil had no structure as a result of downward pressure by either machinery or animal hooves.

“It is most commonly associated with cropping. In sugarcane it has been measured as causing a 15 per cent reduction in yield.

“As sugarcane is essentially a row crop, controlled traffic, which matches the row spacing to the wheel spacing of all machinery used in a cane field, can be one way to prevent compaction on the mound.”

The Reef Catchment investigation looked at controlled traffic on 1.83 m row spacing using GPS guidance. This system proved to be effective by restricting compaction to the interrows.

Mr Muller said the good aggregation in the mound, that is completely made up of small fine peds, meant the roots were able to grow throughout the mound and down into the subsoil. Whereas in the compacted interrows, very few roots were able to penetrate the compacted layer He said looking to see where the roots are able to grow is another way to check for compaction.

“Soils vary in their natural ability to have structure and it is related to clay content. So sandy soils with less than 10 per cent clay do not have any structure as there is insufficient clay to bind the soil together to form the natural soil aggregates or peds,” said Mr Muller.

“This could be contrasted to a black cracking clay soil formed on basalt, such as occurs on the central highlands. This soil, which has up to 80 per cent clay, is completely made up of small, fine peds. In between these two extremes, the amount of soil structure gradually increases as the clay content increases.”