Slurry utilisation on grass

Published 13 February 15

Utilise the value of slurry

Now the NVZ closed period has finished for all soil types and land is drying up well, the opportunity to utilise the value in slurry should be part of routine spring work across all farms, says Chris Coxon, member of The Farm Consultancy Group.

For those who are farming in NVZs, it’s important to remember that slurry can only be applied in a single application of 30m3/ha or less until the end of February. If you have applied slurry earlier in the season there must be a three week break between applications. 

It is now well publicised that slurry has a useful value so the challenge is to tailor applications to both what is actually in the slurry store, and what the crop requires. The drier winter is likely to mean that the slurry is widely different in nutrient value than it was last season. Therefore, applying the same rates year after year is fine but the duration nutrient is of value to the crop, should be considered.

The amounts of nitrogen, phosphate and potassium in slurry make it an ideal nutrient for applying to crops for ensiling. Grass and maize are bulky crops which have a high demand for potash and therefore, are the crops that should receive the bulk of applications where possible.  They are also the crops that can provide cost savings, with ‘standard’ slurry having a value of around £3-4/m³ in available nutrient. This can soon equate to £120/ha for a 40m³ application. It is worth taking the time to calculate what the crop is receiving from slurry, and then save money on artificial fertiliser whilst still fully feeding the crop.

For example, a 40m³ application of 6% DM slurry in March will contain 104kg of nitrogen, of which 48kg will be readily available to the plant. Compare this to a 2% DM slurry which provides 36kg of nitrogen and the differences can easily be seen. Both slurries provide useful amounts of nutrient, but for matching a first cut silage requirement of around 100kg of nitrogen, there would be a difference of 10% in the nutrient supplied if you follow the same slurry and artificial fertiliser plan each year.  

While it is important to feed the crop well, ensuring that low amounts of nitrate-nitrogen are present at cutting is vital to allow for good quality fermentation. In an ideal situation, it would be best to mix the slurry store well, apply an even rate across all silage fields as accurately as possible and then get a sample of what has been applied analysed. The turnaround time for slurry analysis is a matter of days and, from this, artificial fertiliser rates can be tailored to crop requirement. 

The break of around one week between slurry applications and artificial fertiliser is also important as research highlights that close timings will increase the amount of nitrous oxide emissions from the interaction of nutrients. This is both non-economic and bad for greenhouse emissions.

The cut in milk price on farm is tuning the mind for all systems and the opportunity to feed the crop correctly to produce top quality forage, while making financial savings should be on the priority list on all farms this spring. 

For more information see chapter 11 of Grass+ ‘Optimising fertiliser practise’ and worksheet 14a and 14b of Grass+.