There is insufficient evidence to change autumn nitrogen (N) guidance for no-tilled cereal and cover crops, according to an AHDB-funded review of public and industry data.
The AHDB Nutrient management guide (RB209) states autumn N applications should not be applied to winter cereal and cover crops, irrespective of the cultivation system.
According to findings from a limited number of research trials available in the UK, sufficient N is mineralised in most situations to fulfil crop N demand during the autumn and winter.
The conclusions were made as part of an AHDB-funded (£15,000) three-month review.
Led by ADAS, the review focused on the autumn application of manufactured N fertiliser in no-till situations, especially in similar climatic conditions to the UK. The reviewers looked at the effect of such applications on crop yield and water quality.
Dr Sajjad Awan, who manages nutrient management work at AHDB, said: “We commissioned this review as observational and informal research trial evidence suggested that soil N supply to crops could be insufficient under no-till systems.
“This seemed plausible, as it is known that the rate of N mineralisation is possibly lower in no-till situations, compared to ploughed situations.
“As it is essential RB209 guidance is based on the best-available evidence, AHDB funded this review to see if the guidance needed to be changed to reflect the cultivation system.”
The review confirmed no-till approaches reduced the amount of soil mineral N (SMN) by five to 25kg N/ha and that this, typically, was equivalent to a six to 29 per cent reduction in the autumn soil N supply (SNS).
Very few experiments, however, were identified that looked specifically at the effect of autumn applied N on crop performance and nitrate leaching under reduced-tillage situations.
Three cereal experiments identified did include a no-till treatment and these found no evidence of a positive yield effect. One shallow min-till experiment, however, did show a positive yield response but whether the same response could have been achieved through spring-N application was not tested. The review also found that half of the autumn applied N to cover crops was taken up.
Dr Awan said: “We know yields in no-till situations are more variable but the evidence suggests this variability is likely due to a myriad of factors, with N fertiliser potentially playing a relatively minor role.”
Research review 91 ‘Use of autumn nitrogen in no-till farming systems’ can be found at cereals.ahdb.org.uk/nutrientresearch