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To contact one of our “Forage for Profit” team, call the Seed Office on 01769 576232
or Graham Ragg on 07798 583667
or email

NPK recommendations for silage

To maximise silage yield it is vital to supply the nutrients which the crop requires, this can be achieved with knowledge of your soil fertility. Indexes from recent analyses are important in this process as nutrient applications are depend on the soils latent fertility. The nutrient value, using published figures, of any dung or slurry applied need to be deducted from the totals recommended.

Organic Manures

kg available N P K
Winter surface application      
Farm yard manure 12 tonnes/ha 7 25 86
Slurry 6% DM M3/ha 20 13 69


kg available N P K
Farm yard manure 5 t/ha 6 20 69
Slurry 6% DM 2,000 gall/acre 16 11 56


  • A two cut system can remove up to 10 tonnes of silage DM/Ha and equates to 200 - 400kg of N which needs to be replaced. How much to apply depends on
  • Time of year and residual N in the soil. 
  • The growing period between closing and harvesting but, a total equating to not more than 2.5 kg N /day during this closed period.

Whether the field has been fertilised and grazed before closing or whether slurry was applied in early spring or after first cut.

Generally, applications in total will be between 100 -150kgN/ha (80-120 units/acre) for first cut and 100kg/ha (80 units/acre) for second cut. Remember that heavy applications will both depress the clover and reduce the N contribution it can make.

Phosphate P205

Phosphate is necessary to make the best use of applied N and also to promote root growth and recovery after cutting or grazing. Two silage cuts plus grazing will remove 65 kg/ha of phosphate. For a target index of 2 some building needs to be done if below index 2 and applications for maintenance at index 2.
Depending on soil analysis the quantities required will be; To convert these figures to Units/acre then multiply by 0.8

Potash K2O

Like nitrogen large quantities are removed by each cut and unless replaced both subsequent fertility and sown species will decline. Two cuts will remove 230 kg K2O, and 3 cuts 280 kg.  As above, the target index is 2, below which a build of reserves is necessary but has to be done carefully to prevent luxury uptake in periods of rapid growth.

In all cases the figures below are ‘total’ requirements and must include the Potash for other sources, i.e. slurry, FYM or Specific fertilisers. Potash should not be applied at more than 12.5kg/Ha before grazing, or until the field has been closed for silage.

To convert these figures to units/acre, multiply by 0.8. Note the smaller amount applied for the first cut to prevent luxury uptake, the extra should have been applied the previous autumn. Again don’t forget about the value of K you have applied in the form of animal manures. It is important to bear in mind that these recommendations are focused on 3 nutrients and that there are over 30 involved in growing quality grass.

Options for organic farmers

It may seem on the surface that organic producers don’t have many options when it comes to nutrient balancing. Like conventional producers the nutrients available to the plant are pivotal to the success of grass and clover crops and reseeds.

Mole Valley Forage Services can help with this, starting with a soil test that is specifically tailored to the organic producer. The Grassland Organic soil test looks at pH, P and K but with the addition of the other macro nutrients and targeted trace elements in addition to the clay content of your soil. Depending on the results of your tests and your certification body e can then supply you with fertiliser options that can help increase the likelihood of success from your reseeds and grassland production.


If you would like more information about fertiliser recommendations or a free nutrient plan then please contact your local Forage specialist or call the fertiliser helpline 01769 576405


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