With a straw incorporation scheme in the pipeline, Teagasc looked at some of the figures involved at the first of its spring tillage seminars.

Dermot Forristal outlined that straw generally contains approximately 40% carbon and 20% of that carbon (C) can remain in the soil, so a high-yielding winter wheat crop has the potential to add 500kg of C/ha to the soil.

Apart from the carbon sequestration potential, an increase in soil carbon also means an increase in soil organic matter.

Dermot noted that average soil organic matter contents on tillage soils are 5%, but levels below this are worrying. Chopping straw can help to maintain and gradually increase soil organic matter levels over time.

With the build-up of organic matter comes improvement in soil structure as aggregates hold together better, earthworm numbers increase and water infiltration improves. Better biological functioning and nutrient cycling can also follow.

Approximately 10% of phosphorus (P) applied to cereal crops is contained in the straw, while approximately 50% to 60% of potassium (K) applied ends up in the straw.

In an oat crop (yielding 9t/ha) for example, 3.6kg/ha of P and 87kg/ha of K can be returned to the soil through the straw.

With those nutrients valued at approximately €82/ha and oaten straw often a hard sell, this may be a really good option for many.

Soil treatments

As a comparison, Dermot looked at how other soil treatments can affect soil carbon levels. As mentioned already, winter wheat straw can deliver 500kg of C/ha.

Farmyard manure (applied at 20t/ha) can contribute approximately 300kg of C/ha. An application of 25,000l/ha of slurry can deliver approximately 50kg of C/ha, while a cover crop which produces approximately 3t DM/ha can return approximately 250kg of C/ha.

Key management practices

Two key things need to happen when straw is incorporated. Firstly, the chopper must distribute the straw evenly over the soil. The next thing is that where soils have low levels of biological activity and low earthworm numbers, the straw should be incorporated as soon as possible in order to start to break down.

Farmer view

In some cases, straw does not need to be incorporated using a cultivator.

Speaking on the Teagasc webinar, Patrick Mulhall, a farmer in Tullow, Co Carlow, explained that he began chopping straw when he lost sugar beet from his rotation and was growing continuous cereal crops.

Patrick noticed his crop yields were deteriorating and started to chop and incorporate straw to improve soil health.

Patrick direct drills on his farm, so the straw is incorporated by the earthworms. Straw is spread on the surface and earthworms break down the straw while incorporating it into the soil.

An examination revealed his soil structure has significantly improved. The soil is crumbly, earthworm numbers have increased and Patrick’s input costs have declined, particularly P and K. He attributes some of this reduction to straw chopping.