Nutrient planning to optimise silage quality
Producing high-quality silage starts long before the mower enters the field. Careful nutrient planning is key to maximising the yield and feed value potential of your grass or forage crop.
Balancing nutritional inputs
A well-balanced nutrient strategy supports strong crop growth, driving higher dry matter (DM) yields and improving the energy and protein content of the silage – both of which are crucial for livestock performance.
Getting nutrient levels right also plays a vital role in ensuring good fermentation at clamping, which helps minimise waste and maintain feed quality throughout the season.
However, applying too much or too little fertiliser can lead to problems.
Over-fertilising increases the risk of lodging and can cause excess nitrogen in the crop, which affects fermentation.
Under-fertilising, on the other hand, limits yield potential and reduces the overall quality of the silage.
By focusing on the nutritional needs of your crop, nutrient planning can deliver a better return on investment and more productive, sustainable silage-making.
Assessing your silage crop’s needs
Understanding your soil and crop is the first step in building an effective nutrient plan.
Without this, you risk facing unnecessary costs, poorer silage quality, or avoidable environmental losses.
Regular soil testing is essential to get an accurate picture of your soil’s ability to grow crops, utilise nutrients, and produce a silage crop that will perform in and out of the field.
Testing every three to five years will give you a clear view of key indicators such as pH, phosphate (P), potash (K), magnesium (Mg) and organic matter levels.
For soil pH, the ideal value for grass leys is 6.0-6.5, while the target value for clover-based swards, which are more sensitive to soil acidity, is 6.2 or higher.
Maintaining pH within these ranges ensures nutrients applied to the soil are available to the crop, rather than being locked up and wasted.
Our top tips on addressing soil fertility are here.
Once you know your soil indices, you can calculate the nutrient offtakes – how much nutrient is being removed from the field when you cut and remove silage.
On average, each tonne of dry matter (DM) silage removes:
| Nutrient | Offtake per tonne DM silage |
|---|---|
| Nitrogen (N) | 25-30 kg |
| Phosphate (P₂O₅) | 4-5 kg |
| Potash (K₂O) | 2530 kg |
| Sulphur (S) | 23 kg |
(AHDB Nutrient Management Guide (RB209))
Knowing these figures allows you to plan replacement applications that replenish the offtakes.
This will also help to avoid the risk of nutrient deficiencies or the unnecessary build-up of nutrients that could be lost to the environment.
Nitrogen to drive grass growth
Nitrogen (N) is key to maximising grass growth and silage yields.
AHDB RB209 recommends applying 100-120 kg N/ha for first cut silage, depending on sward age and previous fertiliser use.
Apply in early spring once soils are around 5°C and allow at least six weeks before cutting for full uptake.
If applying slurry or manure, adjust fertiliser rates accordingly –for example, 30 m³/ha of cattle slurry can supply around 30 kg N/ha of readily available nitrogen.
To read more about how to improve nitrogen efficiency, check out this blog post.
Phosphate and potash for early establishment
Balanced applications of phosphate (P), potash (K) and sulphur (S) are just as important as nitrogen to support strong root development, nutrient uptake and crop quality.
Phosphate (P) supports root growth and early-season establishment, while potash (K) helps regulate water movement and improves drought tolerance.
For first cut silage, RB209 recommends the following rates:
- P₂O₅ (Phosphate) – Typically 35-50 kg/ha
- K₂O (Potash) – Around 90-120 kg/ha
Exact rates should be adjusted based on your soil indices and expected offtake.
For example, silage removes around 25-30 kg K₂O per tonne of DM, so heavy-yielding crops will need higher replacement rates.
Sulphur supporting silage quality
Sulphur (S) is often overlooked but plays a key role in supporting grass protein content and improving nitrogen use efficiency.
For silage, RB209 advises applying 25-40 kg SO₃/ha per cut, particularly on lighter soils or where slurry applications are low.
A balanced nutrient plan, aligned to these RB209 recommendations, will not only boost yields but help improve silage quality and sustainability.
For more information on preparing grasslands throughout the year to maximise productivity, check out our recent blog here.