For regenerative farmers, straw provides a valuable source of organic matter for improving soil health, but it can also bring crop establishment problems if not managed correctly.

Straw holds important nutrient qualities which are valuable to the soil. “The value of the phosphate and potassium it provides roughly translates to £20/ha,” explains Charlotte Cook, independent agronomist at Indigro.

“But it’s obviously worth considering the organic carbon too, which is important to build the soil health and soil biology.

“There is also the fact that by keeping the stubble intact, this provides the soil with some protection over winter, as well as avoiding soil erosion and nutrient runoff.”

See also: Can arable farms operate without fossil fuels?

Direct drilling offers benefits including less soil movement, reduced weed burden including blackgrass, carbon sequestration and lower fuel use. But it’s important to get straw management correct before going in with the drill, and that begins with the soil.

Soil biology

If the soil is in good working order, the straw will break down quickly.

“Do a visual assessment; dig a hole, see if there are layers of compaction, how active the worms are, whether the roots go down three inches, or are in horizontal bands,” Charlotte says.

“If there is compaction, or if it’s waterlogged, that will need to be rectified before thinking about direct drilling.”

It’s easy to see which soils are not active, as the straw will still be sitting on the surface two to three years later.

“The difference of getting the soil right before drilling can be that the straw breaks down in weeks rather than months,” she says.

Harvesting

Chopping straw can add a layer of armour to the soil, helping to improve moisture retention and reduce erosion.

But poor chopping and uneven spread can lead to issues with establishment, particularly where patches of thick straw harbour slugs.

With bigger combines come bigger headers, and some may struggle to spread the straw as far as necessary.

“The straw needs to be spread the width of the header ideally; the newer combines have good spreaders, but some of the older ones don’t,” says Charlotte.

“If the chaff from the previous crop isn’t thrown far enough, it builds up in the same place every year, and slugs often live in that band, too.”

The other thing to note is that chopping straw takes quite a lot of horsepower, so it is an expensive thing to do, she says.

“So, minimise the length and volume of the straw by growing shorter-strawed varieties or using plant growth regulators, otherwise it burns lots of fuel just combining and chopping.”

© Maciej Bledowski/Alamy Stock Photo

Straw raking

What can be done if a good spread hasn’t been achieved? “Straw or stubble raking is an option to help distribute the straw and start the breakdown by incorporating it with the soil,” says Charlotte.

“The quicker it can be incorporated, the better, because the microbes and worms can start to access it and pull the carbon down.”

Ensure the carbon-to-nitrogen ratio is known, too. “If you’re chopping straw year-on-year, you want to be careful that you’re not just building up the carbon without addressing the nitrogen,” she adds.

“You can get carbon choking, which can affect the following crops.”

This happens when carbon levels rise, and the carbon-to-nitrogen ratio is off. This means the following crop will be unable to access enough nitrogen.

Grazing an understorey in the rotation can be beneficial. “If there’s an understorey of white clover, livestock can graze that down from August into September, which is great because the manure will help to break down the straw, as well as introducing more biology into the system,” says Charlotte.

Disc drills

When it comes to drill selection, there are some advantages and disadvantages to the various options. “A disc drill possibly retains more moisture, but can risk hair pinning,” she says.

This is when the straw lying on the surface of the ground is pushed into the soil in a V shape by the drill. The seed then sits in the V.

“It’s quite a hostile environment for the seed, because it can’t get any soil contact, and there’s a lock-up of nitrogen too,” she explains.

This can exacerbate a slug problem, as it forms a channel in which the slugs can thrive. “However, the advantages of a disc drill are moisture retention, and less disturbance of the soil from a blackgrass point of view.

“It may be worth increasing the seed rate to compensate if it’s going into a slightly less hospitable environment.”

Disc drills also have different disc angles. “There are discs which virtually go straight down and cut through the soil without moving much, but they can sometimes struggle to shut the slot in adverse conditions,” says Charlotte.

“This can be combatted by angled discs, which can improve seed-to-soil contact but will cause more disturbance.”

© Tim Scrivener

Tine drills

With a tine drill, the straw is ripped apart, leading to a less hostile environment for the seed. “It also lets a bit of air into the soil, mineralises some nitrogen and is less likely to have hair pinning and to harbour slugs – but be warned, they can still be there,” she says.

But with moving the soil, the risk of weed germination is higher, and there is more soil moisture loss. “One thing to watch out for is dragging the straw, if it’s not spread evenly. It’s possible to end up with clumps of straw and this can lead to poor establishment,” adds Charlotte.

Depth of drilling is another consideration, particularly when it comes to pre-emergence herbicides.

“Most herbicides specify that they need to be 32-40mm in depth and well covered,” she says.

But when it comes to planning establishment techniques, it’s all dependent on soil type and situation. “Consider which drill would suit the soil the best, thinking about the compaction, drainage and soil biology,” she explains.

And be flexible. “There might be a plan, but it might change with the weather or circumstances. Having flexibility, ideally in drills but also in systems, is really helpful to adjust to the season.”