Adjust main season nitrogen use this spring?

ADAS scientists have brought together new and topical information to help farmers make correct nitrogen decisions this spring/summer. The full text of the advice can be downloaded below.

Allthough targetted for farming practices, these basic principles may help groundsmen and greenkeepers to understand the roll of nitrogen in soils

Summary

• Some winter sown crops are so forward this season that some growers have already completed their planned application of nitrogen. For those that haven't, the main message, even in dry conditions is not to deviate from planned total nitrogen applications, taking into account manure nitrogen supply (from any manures applied since last harvest) and soil nitrogen supply (SNS).

• Correct nitrogen decisions need the SNS to be assessed as accurately as possible. Soil nitrogen is 'free' nitrogen, so it is worth taking SNS into account, especially when it is likely to be much higher or lower than normal. SNS can be assessed using the Field Assessment Method (FAM) or, when SNS is expected to be high, by sampling and analysis using the Soil Mineral Nitrogen (SMN) Method.

• Winter rainfall to 30 March has been well below average in Southern, Central and Eastern England, but above average in parts of South West England, Wales, North West England and Western Scotland. In the drier (mainly arable) areas, N leaching losses this winter are likely to be lower than normal. When combined with poor 2011 crop performance and a mild autumn/winter, this is likely to result in a higher than normal SNS situation. It has never been more important to consider last year's crop performance and the weather since harvest when deciding on how much N to apply - make sure you use the correct N Index table in the Fertiliser Manual (low, moderate or high rainfall). Many growers in Southern, Central and Eastern England should be using the low rainfall table (Table A) in the Fertiliser Manual, but it is also very important to consider crop appearance and previous manure use.

• Data gathered by ADAS as part of the Defra-funded NIT18 project indicate that autumn 2011 soil mineral N levels (before winter leaching) were similar to or higher than the long term average. When using the SMN (measurement) method it is vital that any overwinter uptake of nitrogen by the crop is also assessed and allowed for at the time of sampling, especially in advanced winter oilseed rape crops which usually contain a large quantity of N - this is nitrogen that might otherwise have leached. The amount of nitrogen in the crop (and in the soil) should reduce the amount of nitrogen fertiliser that needs to be applied.

• Remember that the effect of past cropping and organic manure use will usually have a much more significant impact on SNS than seasonal factors such as rainfall or temperature. Fields with a history of manure use will usually have higher SNS levels than those with no manure use history.

For full details of this advice, please download the free document. If you have any queries, please contact the ADAS customer services line on 0845 766 0085 or email enquiries@adas.co.uk .

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