A survey of nitrogen levels in soils by Scottish Agronomy suggests a large proportion of Scotland’s winter barley area does require autumn nitrogen, despite current Nitrate Vulnerable Zone guidelines suggesting responses would not normally be attained.
Autumn-applied nitrogen is allowed during the NVZ closed period provided an economic yield benefit is expected because of the crop’s requirement – the general rule from SEERAD is in soils with less than 50kg/ha available nitrogen in the top 30cm.
However, SEERAD NVZ guidelines state that it is not normally required.
But Scottish Agronomy’s survey in the autumns of 2004 and 2005 showed most cereal stubbles contained very low levels of available nitrogen, says the firm’s Allen Scobie.
“In 2004 all 24 farms tested were below the 50kg/ha N threshold.”
That was purely on arable farms. A larger survey of 262 farms in 2005 was split about evenly between purely arable farms and livestock farms where organic manure was used.
“On the arable farms, 90% were below the threshold,” says Mr Scobie.
“Even on livestock farms, where there was a much greater range of levels, two-thirds were below.
“It gives the message that not applying autumn nitrogen could be detrimental to Scottish agriculture.”
Further evidence of the response to autumn nitrogen came in small plot trials where 40kg/ha N was applied in autumn 2004 to four varieties.
“The average response was 0.85t/ha,” says Mr Scobie.