Advice on draining and restructuring waterlogged soils

The best way of draining waterlogged soils and restructuring compacted areas is to plant a crop as soon as it is feasible, and allow them to transpire the water out.

Soils expert Philip Wright, director of Wright Resolutions, says that beyond checking drainage and planting a crop now, remedial work should be left until conditions are better.

Drainage

The first step growers should take this spring to restructure their soils is to check to see if there is any visible areas of ponding or flooding.

If soils aren’t well drained, this might be due to natural seasonal waterlogging, or it might indicate that drainage is not working as it should.

See also: How to increase beneficial insects in arable crops

“Start with ditches, clear them and allow water to move,” says Mr Wright.

“If there is standing water in one area and it’s much lower elsewhere, this should ring alarm bells.”

There should also be a good area of clearance below the outlet pipe.

“It sounds basic but fields with poor drains are always in a worse state.

“Drainage is fundamental – if you can do nothing else, check ditches and drains.”

Pump out with plants

Planting some kind of crop in waterlogged soils and pumping out the water through transpiration is the best option for removing water from poorly draining soils.

This may be a commercial crop, but it may also be a cover.

“At some point, growers need to ask themselves if they are going to make a profit.

“I think it is worth doing the maths, it’s unpalatable but necessary,” he says.

Growers need to compare the likely profit achievable from a spring crop in comparison to the cost of establishing a cheap cover.

This will draw moisture out and potentially get soils in a state where a high-yielding winter wheat crop is possible next season.

If, after doing those figures, it still makes sense to plant a commercial crop this year, growers should work soils shallower than a grower might want, as it dries from the top down.

“Ideally, we would want to work deeper, but just tickle the surface and get it in.

“This is about accepting a bit of compromise.

“The shallower you work, the drier it will be, causing less damage and a better chance of a seed-bed,” he says.

If a commercial crop is not a viable option, then drill a cheap cover, even if there are deep ruts in the field.

Going shallow with cultivations may not even reach the bottom of ruts, but growers must accept compromise at this stage.

Later in the season, soil will be drier and problems at depth that are preventing drainage can be sorted.

“Get the spade out, check the establishment and maybe use the opportunity before autumn drilling to restructure.”

Growers may want to pull a sward lifter through as they would on grassland to allow roots to go deeper to open up the soils.

“Use a crop to fix soils. Metal will help roots, but it’s roots that will fix soils.”

One thing growers can do now is to check for barriers to water movement, as any water that is held up will be very visible at the moment by digging with a spade.

“Start to decide where we are going to remediate when conditions are suitable.

“Default to roots putting it right, or otherwise go in with minimum cultivations.”

If cultivations are needed, the focus should be on lifting and loosening using low angles, not pushing and compressing.

Tines should not be too big, although also not pencil narrow, and if a machine is pulling slots or clods, it will not be doing an effective job.

Weight versus pressure

Soil is at its most vulnerable when it is wet, as its strength is related to moisture, so growers should look to reduce weight and pressure to the soils.

Use light machines, if possible, and reduce tyre and track pressures to the safe minimum limit.

Reducing weight will not necessarily reduce pressure, as removing the balancing weight from the front of a twin track crawler will cause is to sit on its back sprocket, applying a lot of pressure to soils.

River flooding

Flooding by rivers that have burst their banks can look worse than it is, says Mrp Wright.

As soon as water levels have dropped, get out and dig to check how anaerobic soils have become due to pressure, and look to get something in as soon as possible.

How quickly soils will recover will depend on soil type – if it is quite resilient but is prone to slumping, then growers should be able to loosen them quite soon after the flooding.

“If growers can do something then it is back to the principle of depth, they might have to do it in two stages.”

Case study: Herefordshire grower hopes to drill once flood recedes

Herefordshire grower Martin Williams still plans to crop his whole farm despite some 34ha being flooded this week.

Martin Williams' flooded fields

After the floodwater recedes, he hopes to be able to grow a crop of large blue peas on the land next to the River Wye at Fownhope, which was originally destined for winter wheat.

The area first flooded two weeks after potatoes were lifted in the autumn, preventing Mr Williams from drilling his intended crop.

“It would have been wheat, and we would have lost it because of the floods,” he says, as the fields have repeatedly flooded over the winter and autumn due to relentless rainfall.

“All through the winter, we have been thinking that we will plant wheat, because that is what farmers do, but we have decided in the past three weeks that it won’t be wheat, we will put peas in instead.”

While the river floods quickly, it retreats equally as fast and the loamy soils drain well, but despite this, Mr Williams could not see how the area could be drilled with wheat before April.

Peas were already in the rotation as a breakcrop alongside maize – for forage and AD farms – and potatoes, after Mr Williams gave up on growing oilseed rape due to flea beetle pressure.

By growing large blue peas on contract with merchant Dunns, Mr Williams will have chance to rectify drainage channels and properly prepare the soil before he needs to drill.

Before drilling the peas, Mr Williams plans to go in with a Sumo to sort out the compaction left behind by the previous potato crop.

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