Why soil care could unlock wheat yield plateau

Growers need to invest more in their soils and challenge current thinking if they are to break through the winter wheat yield plateau.

They will need to improve subsoil compaction, reverse falling organic matter and improve ageing drainage systems, say soil specialists.

“There is a strong case for reducing intensity of tillage operations and increasing organic matter inputs in the future in order to improve long-term soil health and yield stability,” says Elizabeth Stockdale of Newcastle University.

See also: Video: Grow your yields and guard against crop disease with compost tea

Crop rooting

Compaction not only reduces root growth, but slows the “biological engine” of the soil which limits release of nutrients, while decomposition of organic matter from crop residues and manures becomes less efficient.

“Soil should only really be moved when absolutely necessary,” Dr Stockdale adds.

Getting the right balance of big and small spaces between soil particles is key, not just for drainage and root growth, but because it is in these pores that most of the biological activity takes place.

“Without good soil structure the plant’s ability to grow is severely compromised – especially at the extremes of soil texture – such as in soils with low clay content where it is harder to build up a reservoir of organic matter or in heavy clay soils which become oxygen-deprived very quickly,” she says.

Michael Horsch, founder of the eponymous machinery group, says roots have evolved over millions of years to encounter slowly increasing density the deeper they go, so sudden changes in density created by ploughing works against plants genetics.

Trials have shown four times as many earthworms in no-till systems compared with ploughing, which is a good indicator of soil health. But he questions a no-till future in northern Europe.

“For no-till to work you need crop residues that break down quickly and wheat is among the toughest for bugs to digest,” he says.

The north European climate doesn’t help, with only 250 days a year suitable for decomposition and wheat stubble needing 500 days to break down properly.

But even the option of min-till is not without problems, as a mulch pan at 7.5-10cm is as bad as a plough pan at 300-375cm with much the same effect on root development.

Ironically, one of the best aids to cultivation and organic matter decomposition on the farm today are large combine harvesters.

“Your 400hp combine with a straw chopper on the back is the best decomposing agent we now have,” he says.

Tudor Dawkins

Tudor Dawkins

Tudor Dawkins, technical director at distributor ProCam, challenges the view that ploughing could solve many of the issues with soil health.

“We know that soil compaction can reduce wheat yields by 15-20% and this could be the cause of the variable yields we seem to be experiencing,” he says.

Some growers turn to ploughing to control blackgrass, but he suggests growers should think if they really need to plough and, if so, when it should be carried out.

“Burial of blackgrass seeds to greater than 5cm will prevent germination, but inversion needs to be thorough,” he says.

The seed needs to be buried for at least three years in order for this method to provide effective control.

Where deeper compaction problems exist, Dr Dawkins recommends getting the spade out and looking for where the problem occurred.

“Don’t work too deep – the aim is to disrupt the compacted layer just below where it lies. In this way problem areas are addressed but fuel consumption is minimised too,” he says.

Dr Dawkins adds that drains and outflows should be checked to ensure water can get away from fields and mole drains should be considered on suitable soils.

“Traffic should be minimised, especially when conditions are ‘difficult’, with particular care required at harvest,” he says.

A soil pH of about 6-6.5 is essential for optimum availability of a range of vital nutrients, so testing soil and applying lime to correct acidic soils is essential.

Farnon Ellwood from the University of the West of England says growers in ProCam’s 4Cast crop production database who delayed drilling to control blackgrass were often able to get high yields.

“Where farmers were able to delay drilling, for example to get on top of potential blackgrass problems, those crops drilled later than the norm were some of the highest yielding of the year,” he says.

Speakers were delegates at last month’s ProCam Soils Conference, “What is a healthy soil?”

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