Grassland nitrogen is at a 20-year low – but could still go even lower

Even with nitrogen use on grassland having fallen in 2004 by 6kg/ha, there is still room to reduce inputs further.

Average N use in 2004 hit its lowest level since the early 1980s with applications averaging 77kg/ha, according to results from the British Survey of Fertiliser Practice.

Such data are now being recognised by farmers as a resource with which to benchmark their practice against others in equivalent farming situations and against latest Good Agricultural Practice guidelines, reckons Jane Salter of the Agricultural Industries Confederation.

The survey reports that nitrogen applications in Great Britain rose by 3kg/ha on field crops, but decreased by 6kg/ha on grassland, she explains.

“Overall phosphate fertiliser rates increased by 1kg/ha on both field crops and grassland, while potash rates also increased by 1kg/ha on field crops, but were unchanged on grassland.

Although this decrease in nitrogen use is encouraging, there are further steps to decrease future use, reckons John Morgan of Creedy Associates.

“The potential of organic manure still needs to be realised, particularly as nitrogen costs continue to rise.”

And achieving a good establishment of clover can also reduce the need to buy in bagged nitrogen as it can provide 170-200kgN/ha, he adds.

But even though reducing nitrogen use is advisable, he reminds producers of the importance of soil analysis to assess pH levels.

“Where grass pH should be about six, analyses are regularly coming back at about five, indicating significant losses in yield.”

In this instance applying lime instead of expensive nitrogen could correct the balance, he explains.

And with a reduction of sulphur coming from the atmosphere of about 85% in the last decade, grass is becoming short of sulphur at the start of spring.

“Grass will appear yellow in colour, indicating lack of nitrogen, but a grass sample sent off to the lab is likely to show a lack of sulphur.”

Berks-based farm manager Mark Osman says he has managed to reduce his fertiliser use by up to 25% in the last 18 months.

“We were applying about 310kg/ha but started targeting slurry use, regular soil testing to come in line with cross compliance issues and developed a nutrient plan.

“We were also fortunate to take advantage of high reserves of P and K from cow grazing, which helped reduced nitrogen requirements,” he adds.

But Mr Osman admits he still uses a monthly application from March though to the end of July, which is still proving economic at 153/t.

But, even though producers are being encouraged to reduce nitrogen use on grassland, the overall cost of N use accounts for about 0.7-0.8p/litre, which is relatively small when you consider labour at about 4.5p/litre and power and machinery at about 3.5p/litre.

“So applying nitrogen at the optimum rates can still prove economic,” he reckons.