As one Defra agency appears to be finally learning the painful lessons of IT rollouts gone wrong, another seems to have walked into the same trap. Defra fertiliser manual 'a step forward'
THE new fertiliser manual from Defra - the eighth edition of RB209 - is a ‘big and brave step forward’, says GrowHow UK’s grassland specialist Elaine Jewkes.
She says the new edition recognises that farmers do not follow one single system and these different systems have different fertiliser requirements.
“While this is particularly true in the dairy sector it is also relevant in beef, and to an extent in sheep farming,” says Miss Jewkes.
“For many years a common question from grass farmers has been, ‘How much N do I need to apply for my system?’ - and it’s something we’ve struggled to provide an answer for. The result has been that farmers have been using trial and error to find the amounts of nitrogen that will provide the results they want.
“That’s fine on an individual farm, but it doesn’t help other people to work out what to do,” says Miss Jewkes.
The new RB209 goes a long way towards addressing this issue, by following a scientific approach to objectively quantify the fertiliser that may be needed in a given grassland system, according to the target level of production.
David Chadwick from Rothamsted Research, North Wyke (formerly IGER), explains the new approach: “The overall approach is no longer based solely on the Nopt (the economic optimum N rate) for grass growth. It now takes account of the need to supply sufficient home grown forage for particular animal production systems, at different levels of intensity of production, stocking rate, and concentrates use. It therefore allows farmers to obtain relevant recommendations for whole season total nitrogen requirement.”
The N recommendations are based on standard values of daily liveweight gain, forage intake and feed energy conversion to milk, proportions of available land devoted to cutting and grazing as well as efficiencies with which home-grown forage can be utilised under the two harvesting regimes (cut and grazed grass).
A new analysis of existing national multi-site nitrogen response data for UK grassland has been used throughout. There is also improved guidance on nitrogen contribution from clover, based on photographic recognition of percentage cover in the sward.
“The tables in the Manual use information that farmers and advisers will know, such as stocking rate, feed rate and milk yield, so any farmer can reasonably easily identify where they fit in,” says Dr Chadwick.
Miss Jewkes says the new approach is ‘quite a substantial change’ and may take a little more effort to use initially - but that effort will be well worthwhile. The splits of fertiliser need to be worked out through the season and some basic adjustments are needed where a particular stocking or feed rate is not specifically listed in the tables in the manual - see examples.
She says: “The new manual is a welcome step forward in trying to provide what farmers want and need in modern grassland agriculture - fertiliser recommendations that are relevant to their systems. Yes, it needs a bit of thought at first, but what new thing doesn’t?”
Example 1: A dairy system based on grazed grass
- 6,800 litres per cow at a concentrate rate of 1.7t per cow and a stocking rate 1.9 LU per ha
- Historically, fertiliser use has been more than 250kg N per ha and the grass growth class average
- Using the manual this gives an N rate of 340kg N per ha, but the SNS is high so we have to subtract 30kg N per ha and a further 20kg per ha needs to be deducted because the concentrate use is 1.7t per cow, not 1.5t per cow as in the table
- This leaves a total of 290kg N per ha for the season
- This could be applied as either six equal splits of 48kg per ha, six splits weighted towards best growth (50kg, 50kg, 50kg, 50kg, 45kg, 40kg) or seven splits 40kg, 50kg, 50kg, 50kg, 40kg, 30kg, 30kg
Example 2: A beef farm with one cut of silage followed by grazing
- A stocking rate of 1.3 LU per ha, feeding 0.2t concentrate per head per year with average grass growth and moderate SNS
- The manual allows you to work out the N rates for the silage and the grazed grass, and then there is further advice about how to use these rates to work out what to apply and when
- Cutting: The table does not provide a total N figure for 1.3 LU per ha but it is easy to work out by taking the mid-point between the 1.2 and 1.4 LUs to come up with 300kg N per ha. But this figure is based on feeding 0.4t concentrate and only 0.2t of concentrate are fed so 2x10kg N per ha extra N is required, giving a total of 320kg per ha for a silage system
- Grazing: A similar calculation has to be made for the grazed land where the N requirement for 1.3 LU per ha is the mid-point between 1.2 and 1.4, which is 115kg N per ha. Again, because only 0.2t concentrate are fed a further 2x10kg N ha must be added to get the total N requirement of 135kg per ha for the grazed land
- The total N required for a one-cut system followed by grazing is based on these two figures
- For the silage element, 40 per cent of the 320kg N per ha is recommended for first cut, which is 128kg N per ha
- Then for the grazing part of the system you need to pick up the recommended rates from May onwards. These are: May 20 per cent; June and July 15 per cent each; and August 10 per cent. Applying these percentages to the 135kg per ha total N rate, worked out from the table, gives the actual N rates to apply to get the grass needed. In practice, most farmers would probably choose to apply this fertiliser in two applications, one in May at 50kg N per ha and one in July at 35kg
