Archive: SRUC researcher warns of the dangers of soil compaction

Published 11 November 14

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A grassland researcher at Scotland’s Rural College warns farmers that soil compaction can lead to the loss of nearly a quarter of spring grass yields. By taking more care with machinery and livestock they can reduce that loss and cut the farm’s greenhouse gas emissions substantially.

The preliminary results of a three year DairyCo-funded trial on grassland compaction suggest that mechanical compaction (caused by heavy machinery) has a negative impact on yield and the environment. Trampling by livestock, on the other, hand also causes a substantial reduction in yield but appears to have effect on greenhouse gas emissions.

DairyCo research and development manager, Dr Debbie McConnell says: “Soil structure is important because it determines the ability of a soil to hold and conduct water, nutrients, and air necessary for plant root activity. Compaction arises when soil particles are compressed reducing both the air and water space between particles – and the effects of this is what we’ve been studying through our research partnership.”

At SRUC’s research farm in Dumfries, researchers compared un-compacted plots with those compacted by machinery, and by animal trampling. The first grass cut of the year, was found to be the most affected by both types of compaction. While there were slight differences between each year of the trial, the average yield loss in the spring was between 20 to 25% on the compacted land (both animal trampled and mechanical).

The spring cut had a significant drop in yield while later in the year the cuts were not as heavily affected. This is probably due to drier weather conditions and which were more favourable to working on the land without increasing compaction.

In terms of greenhouse gas emissions, there was a significant increase on those plots compacted by machinery. Nitrous oxide is a highly damaging greenhouse gas with a warming potential over 300 times that of carbon dioxide. Researchers found 30% higher nitrous oxide emissions from machinery compaction than those trampled by grazing cows which in turn had only slightly higher emissions than the un-compacted land.

Paul Hargreaves, Grassland Researcher at SRUC’s Dairy Research Centre, who has been leading the study, says: “Mechanical compaction is having a significant effect on nitrous oxide emissions. Higher levels of nitrous oxide were measured from the plots which were compacted by machinery as the soil took longer to lose water and this encourages production of the gas. As tractors and other machines we use on grassland are increasingly heavy, the compaction goes down to a much deeper level.

“Of course, compaction by livestock and machinery will happen, it is part of farming. However, the key message is to consider carefully when you take your tractor out, the wetter the field the greater the chance of producing harmful compaction. It is also important to think of investing in wider, low pressure tyres which will spread the weight and cause less damage. I think this is often more of a problem with trailers which can have quite slim tyres bearing very heavy loads.”

For more information on soil compaction see chapter 10 of Grass+ and the ‘Understanding soil structure’ video on the DairyCo YouTube channel which covers the basics of soil compaction.