Agrassland researcher with Scotlands Rural College is warning farmers that soilcompaction can lead to the loss of nearly a quarter of spring grass yields. Bytaking more care with machinery and livestock they can reduce that loss and cutthe farms greenhouse gas emissions substantially.
Asa three year DairyCo-funded trial on grassland compaction draws to a close theresults suggest that mechanical compaction (caused by driving heavy machineryover land) is detrimental to both yield and the environment. Trampling bylivestock also causes a substantial reduction in yield but appears to have lessof an impact on greenhouse gas emissions.
Thetrial, carried out on SRUCs research farm in Dumfries, compared uncompactedplots with those compacted by machinery, and by animal trampling. The firstgrass cut of the year was found to be the most affected by both types ofcompaction. 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 compactedland (both animal trampled and mechanical). .
Whilethe team did see a significant yield reduction at the spring cut, later cuts inthe year were not as heavily affected. This is probably because the weatherconditions are drier therefore more favourable to working on the land withoutincreasing compaction in the soil.
Interms of greenhouse gas emissions there was a significant increase on thoseplots compacted by machinery. Nitrous oxide is a highly damaging greenhouse gaswith a warming potential over 300 times that of carbon dioxide. Researchersfound 30% higher nitrous oxide emissions from machinery compaction thanthose trampled by grazing cows which in turn had only slightly higher emissionsthan the uncompacted land.
PaulHargreaves, Grassland Researcher at SRUCs Dairy Research Centre, who has beenleading the study, says: Mechanical compaction is having a significant effecton nitrous oxide emissions. Higher levels of nitrous oxide were measured fromthe plots which were compacted by machinery as the soil took longer to losewater and this encourages production of the gas. As tractors and other machineswe use on grassland are increasingly heavy, the compaction goes down to a muchdeeper level.
Ofcourse, compaction by livestock and machinery will happen, it is part offarming. However, the key message is to consider carefully when you take yourtractor out, the wetter the field the greater the chance of producing harmfulcompaction. It is also important to think of investing in wider, low pressuretyres which will spread the weight and cause less damage. I think this is oftenmore of a problem with trailers which can have quite slim tyres bearing veryheavy loads.
Theresearchers also assessed different techniques for improving compacted soilsuch as sward lifting and soil slitting. They found that although alleviationcan improve yield it will only work if done correctly. Sward lifting orsub-soiling for example can actually be quite destructive to root growth so itis best to do this in the autumn, especially on grassland, or not at all. Swardlifting needs to be done at a certain depth, just underneath where thecompaction ends, or it can increase the compaction problem.
Paulsays: Alleviation will improve the structure of the soil, and so improvedrainage. This should lead to a drier soil the year following alleviation,which means the land can be in use for a longer period of time. Yieldimprovements should also follow over time but these tools must be usedcorrectly to have a positive impact.