Proper diagnosis could boost grassland yields

Soil compaction is a common problem on livestock farms, but often goes unnoticed in the drive for higher production at lower cost.  Simple intervention can significantly boost grassland yields and usability.

Many livestock producers consider soil compaction to be the curse of the arable farmer. But that simply is the case. How many grassland farms have the odd wet or poor field? Some may just be that way, but most are caused by compacted soil and can be significantly improved by proper diagnosis and intervention.

Compaction is such a widespread problem that the Environment Agency is trialling a self-help style workshop in the south-west to enable producers to diagnose and address the real issues affecting their soils – and provide a welcome boost to yields and trafficability.

“With milk prices under pressure and increasing cow numbers, soils have come in for a bit of a hammering”, said dairy consultant Janice Radford from Green and Kelly, at a recent farm walk in Devon.

“Healthy soils lead to good crop production, so we need to optimise one of the best resources we have on the farm”.

CORRECT DIAGNOSIS
The Environment Agency’s Richard Smith led the farm walk at Keith Hulbert’s Shermans Farm, Honiton and said the most important thing was to diagnose the soil problem correctly before attempting to address it.

“Half the trouble is that people try all sorts of solutions, like ploughing or subsoiling, without diagnosing the problem in the first place. But once you establish the real issue, the solution should be clear.”

The first thing farmers should do is identify fields with problems, such as water-logging, drought, runoff or poor yields. They should then dig about three holes around the field to get an idea of the variability, at a time when the soil is moist.

“Take off the topsoil first, from a hole about 18sq in,” said Mr Smith. “Then tease the soil apart carefully to reveal the natural blocks with it. It should break apart easily into small, rounded blocks. When they are angular it means they fit together to tightly and water cannot pass through”.

Soil should be friable and small blocks should give when squeezed gently – if you cannot squeeze it together, it is too dense. Plenty of roots and earthworms are a good indicator of a healthy structure – and roots should go down about 1m for grass and 2m for arable crops.

Once the topsoil has been assessed, you should dig out half of the hole to below the subsoil level, avoiding smearing one side so that it can be examined, said Mr Smith. Then use an iron bar to lever out the remaining half, to see how easily the soil breaks apart. “Again, break the soil down into smaller blocks – but don’t force it – you are looking for the natural fissures.” Flat sides are not a problem in subsoil, but large blocks disrupt root growth and drainage.

Often grass fields have good topsoil, but compacted layers underneath – which can be removed by ploughing or sub-soiling, depending on the depth of the problem. These fields often get water-logged quickly and may suffer from drought in summer. Rusty colours in the subsoil are an indicator of water-logging and such wet soils may benefit from land drains.

Soils which are compacted in the topsoil may benefit from a slitaerator to break up the blocks and introduce air pockets, said Mr Smith. Wet and dry layers are also a good indication of compaction – with many soils puddling on the surface, but bone dry beneath the compacted layer.

Maize ground also suffers from compaction, particularly with sandy or silty topsoils, which cap easily when left to stubble. Deeper compaction can also occur from tractor wheelings. “The best way to stop this is to improve soil structure throughout – even cultivated areas can slake when the deeper problem is not addressed”.