Last winter’s heavy rain means many fields have become compacted, leaving farmers at risk of reduced yields in the coming year.

Farmers who grazed livestock outside on waterlogged ground or spread manure on saturated land will have risked compacting the soil, according to Dr Paul Newell Price from ADAS, who was speaking at the British Grass & Muck event in Stoneleigh last week.

Such soil structural damage can restrict root growth and aerobic activity in the soil. “In fields where you think there may be an issue, the first thing to do, once soils dry out a bit, is to get out with a spade and dig a few holes to assess soil structure,” he said.

Each hole should be of spade width, and 300mm to 400mm (12in to 14in) deep.

“Dig out a 300mm thick slice and lift it out. The way it comes out and breaks up by hand are good indicators of how compacted it is.”

Signs of compaction include horizontal cracks, roots growing round angular clods and bad smells, which indicate anaerobic activity where slurry hasn’t broken down. “Vertical cracks are generally good, but horizontal cracks indicate compacted layers.

“Compaction can reduce grass yields by up to 40%, so where there is a genuine issue, it is an important problem to address,” he said. “But it is vital to assess your soils first, as you need to use the right equipment at the right time for the job. Soil structure can recover naturally over time and loosening soils that are in good condition can do more harm than good.”

Heavy rainfall washes the soil particles together, which caps the surface and means that air cannot get down to the plant roots. It is known that grassland is particularly susceptible, whereas most arable seedbeds are coarser and less likely to cap. You need to break up that cap to let the air into the soil; using a spring tine or chain harrow would be ideal.

Capping and shallow compaction up to 50mm to 75mm (3in to 4in) deep, caused by sheep poaching, for example, can be alleviated with a grass slitter/aerator.

Deeper compaction from cattle is likely to be from 125mm (5in) down, with damage from tractors and machinery going down to 250mm (10in). To deal effectively with deeper compaction, you will need to go in with a grassland subsoiler/sward lifter.