Will the chaff deck help control black-grass?


Combine Roadshow

A typical combine dealing with high amounts of straw and chaff

Poop deck, mixing deck, command deck, card deck, Ant & Dec, you’ve properly all heard of.

But chaff deck? Heard of that? No?

Well, at last year’s AHDB Agronomists’ Conference  Michael Walsh, Director of Weed Research at the University of Sydney gave a presentation about said chaff deck fitted to the rear of a combine in order to control grass weed seeds. It’s among other novel technologies used down under to control grass weeds (of which many carry herbicide resistance).

Watch videos of papers at the AHDB Agronomists’ Conference

The idea is to capture the chaff from the back of a combine, arrange it in two rows behind the rear wheel tracks, in a controlled traffic farming system of course. The resulting rows decompose, taking the weed seeds with them, or if not, at least a band type sprayer can deal with any germinating seeds.

The presentation must have hit the spot, because a chaff deck is on its way to Blighty, for trials in some Suffolk winter wheat this harvest. It’s driven of course by the need to combat black-grass.

I will have to own up to being somewhat sceptical about the concept at first sight.

First from an engineering point of view, the sheer amount of chaff flowing from the sieve area of a combine in a British wheat crop is huge compared to an Australian crop. The moisture content is also very different, causing it to flow differently. Would the Aussie system be able to handle our Pommie material? And, yes, in past lives, I have been showered in chaff from combines in both countries among others, so feel qualified to comment.

Secondly, from an agronomy point of view, 95% of black-grass weed seeds need to go into the combine to be gathered into rows for any attempt at effective control. Where are we with pre-harvest black-grass seed shedding? We at AHDB Cereals & Oilseeds do not have good data on this. Add to this, how many weed seeds are carried over with the straw, not handled by the chaff deck?

But, and it’s a big but…in view of having no other bright ideas on the future of black-grass control, with farmers in the worst areas of the country considering continuous spring cropping as a control method, I had to admit it is worth a try.

What other options are out there for the collection and destruction of weed seed happily returning to your soil after being helpfully thrashed out by your combine? You have to admit, combining suits weed seeds very well indeed.

The well-named Harrington Seed Destructor is commercially available in Australia. Drawn by the combine, driven by a 160hp engine it can take the entire crop residue from the combine, feed it into a ‘counter rotating cage mill’ where it is pulverised, weed seeds and all.

French firm Perard has been working on a collector that rolls the chaff into a 700kg wrapped bale. Driven by a 36hp engine the firm believe about 2,000kg/hectare of chaff is collected, meaning between 2.5 and 3 bales per hectare need to be picked up. However, they could have a value in bedding, biogas or burning in farm based straw burners or power stations.

So a trial protocol is being set up. Importantly one of the first things to understand is pre-harvest shedding mentioned earlier, and then carry over via the straw. Then the real work begins on crop residue management. Coming to a Suffolk field this harvest, we’ll keep you posted on progress.



Based at Ashkam Bryan near York, Harry grew up on a beef farm in his native north Wales. Subsequently, Harry developed an interest in farm machinery that took him around the world working in agriculture. Having managed a plant breeding farm near Cambridge for Monsanto, in 2005 Harry joined John Deere as Crop Systems Specialist, from where he was recruited by AHDB Cereals & Oilseeds.

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