Black-grass control – the role of crop nutrition

With black-grass contaminating approximately 54% of cereal crops and, where severe, causing a 50% yield reduction, all methods of control need to be explored, including crop nutrition.

“This is especially true as 97% control is needed to contain this weed’s population,” says Mark Tucker, Head of Agronomy at Yara UK, “and whilst it is widely accepted that cultural controls - ploughing, rotation, and drilling date - are essential components of the black-grass strategy, it is rare to see crop nutrition mentioned in the debate. This, I believe is an oversight.”
Why consider crop nutrition?
Classic research has shown how nitrogen and phosphate impact on a wheat crop, with an increase in leaf number, leaf size and rate of development, tillering and root growth.

“All of these give the growing crop a competitive advantage,” explains Mr Tucker, “and under normal conditions, to optimize yields, wheat will go in around the 15th- 20th September at which time soils will be well aerated, warm and contain available moisture. In such conditions, nutrients – especially nitrogen, sulphur and phosphate – will also be available, with the soil nutrient supply meeting crop nutrient demand. However, where black-grass is a problem, a popular control mechanism is to delay drilling by a month or so.”
Delayed drilling
Whilst delaying drilling can contribute 30% control over Blackgrass, it does leave crops coping with wetter soils that are less aerated. Some soils can be close to field capacity and thus going anaerobic and are cooling down by the day.

“The problem is that these conditions lead to reduced nutrient availability to the growing crops,” says Mr Tucker. “This gives slower growth rates and smaller crops going into the winter. Because the crops are weaker, they’ll offer less competition to the developing black-grass plants. And this is most pronounced on the heavier, clay soils often associated with high black-grass populations.”
How can crop nutrition help?
In this situation, crop nutrition can help in two ways, suggests Mr Tucker: “Crop nutrition can be used to recover some of the crop biomass that has been lost due to the poor conditions and to provide plants with the necessary competitiveness to keep black-grass in check.”

In non-NVZ (Nitrate Vulnerable Zone) areas, autumn applications of nitrogen can be used to speed up leaf and tiller production. However, where NVZ rules apply the focus should be on very early spring applications of an NPKS that delivers fresh nutrients that are available as soon as soil temperatures trigger spring growth. Foliar applications of nutrients should also be part of the strategy to ensure the best possible start to spring growth.

“A competitive crop can provide a further 22% to the control measure of black-grass,” concludes Mr Tucker, “a contribution that no one can afford to overlook.”

LAMMA 2017

Make sure to visit the Muthing stand at the 2017 LAMMA Show.

LAMMA is the UK’s leading farm machinery, equipment and agricultural services show. It attracts in excess of 40,000 visitors from the UK and overseas who come to visit hundreds of exhibitors. The 2017 event marks LAMMA’s 36th anniversary, and is the fourth year it has been staged at the East of England Showground, Peterborough.

Free to attend, LAMMA is open from 7.30am until 5pm on Wednesday 18 January and 7.30am until 4.30pm on Thursday 19 January.

Free car parking for up to 10,000 cars is available.

Register to download our new show app here

Sarah Murray

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