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Soil temperatures should be managed carefully to time fertiliser applications for best results on cereals this spring – especially in barley. Monitor soil temperatures for nitrogen application success

Soil temperatures should be managed carefully to time fertiliser applications for best results on cereals this spring – especially in barley.

Slow-to-climb soil temperatures mean close attention is needed to ensure nitrogen application coincides with the onset of spring root growth and is available for immediate uptake, says Yara agronomy manager Mark Tucker.

Spring growth usually starts once root zone temperatures reach 4.5-5.0ºC – so fertiliser is taken up immediately rather than sitting unused in the soil. This year, however, soils have been tracking 0.5ºC colder than last year – not helped by over-winter water-logging.

“Track your rising temperature proactively,” advises Mr Tucker. “Look at soil temperatures 5-10cm deep because that’s where a lot of root activity is going to happen.

Keeping momentum

“Soil temperature across the country varies, but is generally at its lowest in early January then starts climbing. It can be getting to 4ºC by the end of February in an average situation. Once growth starts, we want to keep that momentum.”

Although temperature monitoring is used commonly for grassland fertiliser applications, Mr Tucker sees scope for greater use in cereals. Accurately-timed early nitrogen is particularly pertinent to sustain the optimum number of ear-bearing tillers in barley.

This is important in hybrid barley because it is sown at a lower seed rate, agrees Paul Roche, technical manager for seed breeder Syngenta. Hybrid barley’s vigorous spring growth responds well to a first nitrogen application at about mid-tillering (GS25).

“Early application allows the already-robust root system to scavenge for nitrogen and other nutrients to really give the crop that early boost. Fuelling hybrid barley’s early-season growth in this way also drives its suppression of grassweeds, such as black-grass, ryegrass and brome.”

Barley guidance

Syngenta started to check soil temperatures at its trials sites a few weeks ago. The aim is to get going just as soon as fields dry out and soil temperatures are in the zone – avoiding applications on soils that are covered in snow, frozen or waterlogged.

Current hybrid barley guidance is to apply 30% of the season’s total nitrogen dose at about GS25, says Mr Roche. This should be followed by 50% at or just before GS31, with the final 20% two to three weeks after the second application, typically by the end of April.

To reduce workloads at the time of the final application, or to boost thin crops such as any recovering from waterlogged soils, an alternative programme of 50% at GS25 and 50% at or just before GS31 is another option.

Water-logging will also have caused soil nitrogen levels to decline, adds Mr Tucker. “As soon as we see water-logging going, so that oxygen is available, that’s normally when we expect to see those first roots appearing,” he concludes.