Plan grass nutrients after poor spring

Soil minerals levels could have been hampered because of the cold and wet spring, experts are warning.

The cold conditions of late could have had an impact – particularly on nitrogen levels – because mineralisation has been hindered.

As a result, grassland farmers are being advised to carry out soil testing to glean more information about their soil nutrient profiles and to check if leaching has caused a reduction in pH.

Fertiliser application

But any fertiliser that is being applied shouldn’t go on at the “full whack rate”, say experts, who recommend application rates should start more modestly.

And as well as the likely effect the wet weather has had on soil nitrates, it’s also expected phosphorus – and sulphur levels – could have been depleted, according to Elaine Jewkes of GrowHow.

“Soil nitrates were at a low level before the winter so after the wet conditions we can expect there’s been an even faster level of leaching than normal. But it’s worthwhile getting a thermometer into the soil because grass won’t start to use nitrogen under 5C.”

In many cases it may be better for grassland farmers not to apply the full whack rates of fertiliser in one application this spring, she says. “It’s too much too soon given the very cold conditions and the soil isn’t in peak condition to really get going and use it.”

“It’s worthwhile getting a thermometer into the soil because grass won’t start to use nitrogen under 5C”
Elaine Jewkes, GrowHow

While phosphorus levels aren’t usually significantly affected by leaching, the extremely wet conditions of the past year may have had an impact, particularly if there were also soil erosion losses.

Ms Jewkes adds: “If your soil test suggests you’ve got a phosphorus shortfall you should make sure you address it in the first dressing within the compound application to try and give things a kick-start.”

“At index two on grazing that would be a phosphate application of 20kg/ha – a little higher on grass for cutting at 40kg/ha. Soil potash levels shouldn’t have been particularly affected by the weather but it’s very difficult to generalise on advice, which is why soil testing is very important this spring,” she explains.

And with soil temperatures still struggling in early April to reach figures usually achieved in late February, any fertiliser that was applied in the brief mild spell in early March isn’t likely to have been of any use to grass and some – not all – will have been leached where soils are still wet.

Ms Jewes suggests going for a fairly modest dressing of N – about 30-35kg N/ha – as though it was an application being made when we are just coming out of winter rather than supposedly well into spring, and then give a second application three or four weeks later.

“It’s important to be aware of how much P and K is available and while sulphur would normally be a higher consideration later in the spring, it’s possible sulphur levels have been badly affected by leaching and lack of mineralisation and so need addressing sooner.

“The priority for this season is to have everything ready so as soon as temperatures start to rise the grass can make immediate use of the nutrients it needs, with no shortfalls.”

Sulphur warning

Shropshire-based consultant Ian Granfield is concerned sulphur levels need watching this spring – despite the traditional seasonal warning about soil sulphur.

“Although it’s often assumed a yellowing of the leaves may be caused by delayed nitrogen uptake, it can also indicate the grass is short of sulphur. I had a case in Italian ryegrass last year and it was staggering to see the effect of sulphur deficiency. So soil sulphur levels need watching this spring and using ammonium sulphate would provide a nitrogen source carrying sulphur.

Even if phosphate levels are OK Mr Granfield says uptake will be impeded by the lack of oxygen in many soils and the low soil temperatures.

“A lot of land has suffered from a lack of aerobic activity because of the extremes of weather over the past year and so oxygen levels have been hit. If ever there was a season where we needed to get air into the land it’s this one so grassland farmers should seriously be looking at pasture aerators to put some oxygen back into their soils,” says Mr Granfield.

While soil nitrate levels have been the biggest victim of the wet conditions, rainfall monitoring in some parts of the UK has shown March to be one of the driest months for some time – despite the intense cold – so some early nitrogen applications may not have suffered severe leaching.

“But I’m convinced this season will sort itself out eventually and first-cut silages won’t be that much later. Care needs to be taken not to apply a second dressing too soon when grass still hasn’t had chance to utilise the first. That situation could create issues,” he says.

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