Arable Monitor soil temperatures for nitrogen application success
S
oil 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 4.55.0ºC – 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. Accuratelytimed 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 blackgrass, ryegrass and brome.”
s
Barley guidance Syngenta started to check soil temperatures at its trials sites a few weeks ago.
Tracking temperatures proactively pays divdends, says Mark Tucker
“
Once growth starts, we want to keep that momentum
Make most of early fertiliser Fertiliser applications will need careful planning after a second consecutive wet winter and varying crop requirements, says agronomy firm Hutchinsons. Indications are that heavy winter rainfall across much of the UK could have increased losses of some of the more soluble soil nutrients, such as nitrogen and sulphur, particularly on lighter, less nutrient retentive soils, so it is important crop requirements are fulfilled as growth increases.
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.
Good potential “We’re still waiting for results from N-Min testing, but my feeling is that given the rain we’ve had, there will be a low reservoir of nitrogen in the soil, and with crops generally showing good potential, it will be vital to protect that from the outset,” says agronomist David Stead. “September-sown wheat looks healthy and well tillered, while even late October and early November-drilled cereals are nicely established with two to three tillers. We need to make sure we can maintain this biomass growth and not compromise the yield potential that’s there.” Main focus Nitrogen is the main focus for early fertiliser as crop requirements increase significantly as canopies develop. Although NMin tests are best done early in the year, Mr Stead says soil testing to gauge the extent of any winter losses can still help inform later applications. Several other nutrients, notably phosphate, potassium and sulphur, influence how efficiently plants assimilate nitrogen. Magnesium is also important as it is fundamental to chlorophyll production and any shortfall reduces photosynthesis, which in turn reduces nitrogen uptake.
MARCH 2021 • MIDLAND FARMER 9
14:53
