With black-grass contaminating about 54 per cent of cereal crops and, where severe, causing a 50 per cent yield reduction, all methods of control need to be explored, including crop nutrition.
That is the view of Yara UK head of agronomy Mark Tucker, who says while it is widely accepted cultural controls – ploughing, rotation, and drilling date – are essential components of the black-grass strategy, it is rare to see crop nutrition mentioned.
“This, I believe is an oversight,” he says.
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,” says Mr Tucker, “and under normal conditions, to optimise yields, wheat will go in around September 15-20, 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.”
But while delaying drilling can contribute considerably to black-grass control, it does leave crops coping with wetter soils which are less aerated, says Mr Tucker.
Some soils can be close to field capacity and soil conditions are thus becoming increasingly 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 winter. Because the crops are weaker, they will 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.”
In this situation, crop nutrition can help in two ways, he adds: “Crop nutrition can be used to recover some of the crop biomass which has been lost due to the poor conditions and to provide plants with the necessary competitiveness to keep black-grass in check.”
In non-Nitrate Vulnerable Zone (NVZ) 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 compound which 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 per cent to the control measure of black-grass,” says Mr Tucker, “a contribution which no-one can afford to overlook.”