Farmers need to start thinking about how much grass is needed rather than just growing it ad lib, according to new guidelines.

The Grass section of the new Fertiliser Manual (RB209) now recommends a systems based approach to applying fertiliser rather than just growing the maximum amount of grass possible, says Mark Tucker, head of agronomy at Yara.

“The guidelines aim to help farmers think more about how much dry matter is needed rather than producing grass ad lib. It is essentially looking at a targeted approach to fertiliser application for individual systems,” he says.

And Mr Tucker believes the changes, which are based on the need to supply sufficient home-grown forage for particular animal production systems at different intensity of production, stocking rate and concentrate use, are good news for the whole industry. “The changes should encourage people to focus on what manures and soils are capable of delivering.”

This approach is also more flexible and relevant to farmers than the previous version of RB209, adds David Chadwick, principal researcher at North Wyke Research, Devon.

“This version provides advice for those wishing to operate at different intensities of livestock production. The higher the intensity the higher the total nitrogen requirement for producing home grown forage and vice-versa,” he says.

An interesting consequence of this new approach is the better the grass growth class of land, the smaller the nitrogen requirement is for producing the target amount of forage, says Dr Chadwick. “This highlights the greater environmental risk of trying to farm poor land at a high level of intensity.”

However, although there are clear benefits to the new approach, at first glance, it will appear to farmers as a much more complicated system, warns Mr Tucker.

“The one downside is the fact it may be more complicated to work through and will need some thought and possibly some assistance from a FACTs qualified advisor.”

Pre-planning before embarking on the recommendations will be essential, he advises. “Some of the critical things to know before working out requirements include stocking rate, levels of clover, grass growth class, concentrate use and output in litres.”

To calculate fertiliser requirements farmers first need to assess the grass growth of their land, says Dr Chadwick. “Identifying the correct intensity of management is the next step and within this farmers need to identify the stocking rate for the coming year for the grass growing area of the farm.

“By using the tables for beef, sheep or dairy you can then work out the total annual amount of nitrogen required to feed stock over the year.” However, where several groups of fields with different grass growth classes are present, they will require separate consideration.”

The total amount of nitrogen required can then be calculated as previously by subtracting nitrogen contributions from Soil Nitrogen Supply, applied manures and fixation by clover, explains Dr Chadwick. “This amount of fertiliser is then divided in to suitable percentages according to timing of applications made over the growing season.”

And by following the new recommendations it could, in some cases, help farmers save money, adds Mr Tucker. “Some people may find out that they have been using too much fertiliser, so may well save on fertiliser costs.”

For more information and to download a free copy of the Fertiliser Manual visit www.defra.gov.uk/rb209. For a hard copy, price £24.99, contact The Stationery Office.