Fertiliser Considerations for This Year’s Silage Ground
Spring is here, and although many of you will still be feeding winter rations, now is the time to start thinking about this year’s silage crop as the days stretch and soils get warmer. Fertiliser prices have until recently been stable, however as fertiliser volatility returns, it is important to plan.
Before applying any product to the grass there are a few important factors to consider, to ensure that the grass will get the best utilisation of the product applied. Knowing the soil’s pH is essential for achieving optimal yield and quality for any crop grown in the soil. Optimum soil pH varies slightly depending on soil type and cropping system for young grass destined for cutting grown in a mineral soil you should aim for a pH of around 6.2. It is advisable to have a soil sampling plan in place, sampling all fields routinely every five years to monitor the soils pH, phosphate and potash levels. This will help to develop a fertiliser plan suitable for silage crops.
Nitrogen is the first nutrient that comes to mind for many when thinking about fertiliser application, applying it at the correct rate will ensure the best optimisation from the grass. For a first cut silage crop it is recommended to apply 120kg N/ha applied eight weeks before targeted cutting date. Higher rates and delayed application can result in the risk of nitrate N in the grass and poor silage fermentation. Applications for subsequent cuts of silage should be made as soon as possible after the previous cut at 90kg N/ha and 70kg N/ha for a third cut.
It is also important to consider sward type when applying nitrogen. If applying to swards with a high clover percentage of clover care should be taken with nitrogen quantity. Clovers are nitrogen fixing crops so naturally help to build nitrogen levels, they are also sensitive to nitrogen and overapplication can lead to other grasses shading the clover reducing the percentage within the sward. Red clover has very low requirements for supplementary nitrogen, if the grass appears nitrogen deficient a low rate of around 50kg N/ha could be considered but should be taken with caution. If you have queries relating to nitrogen application and clover, speak to your consultant for advice. All fertiliser advice should come from a FACTS accredited consultant or agronomist.
Phosphate (P) and Potash (K) levels within the soil can also be monitored through soil analysis. This helps to understand the P and K status and where applications may or may not be required. Phosphate is particularly important for grass establishment; P aids the development of the plant’s roots and the early tillering of the grass. It is particularly important in young grasses as their root systems are not fully developed. An example top-up rate of phosphate on moderate soils would be between 15 and 20kg P/ha, this would maintain a moderate level, however tailored fertiliser applications should be applied depending on soil analysis.
After nitrogen, potash is the second most important nutrient for grass and maintaining M- status is a sign of good grassland management. Offtake levels of potash in grassland can be considerable (180 to 330kg K2O/ha from two or three cut systems) and light or sandy soils can quickly be depleted of potash reserves. Typically, first cut silage rates should be 60 - 90 kg K2O/ha and 50-60kg K2O/ha for second cuts. Exact rates will vary depending on soil status, nitrogen application rate and anticipated grass yield. Where required potash requirements are over 90kg/ha for first any surplus over the 90kg should be applied later in the season to avoid luxury uptake.
N P and K are the three compounds most often considered for silage fertiliser applications, however in a silage cutting situations it is important to consider sulphur applications. The grass cannot use the nitrogen applied to the best of its ability without adequate sulphur levels in the soil. Just like when considering the rates and requirements of N, P and K for the soil, it is important to understand the soil type and its condition before making a decision. Sandy and shallow soils generally would see the greatest deficiencies, along with this fields cut intensively for silage and receiving large doses of nitrogen are at risk. It is important to look at the soil analysis of the silage fields and consult with the farm’s FACTS advisor on selecting a product with the correct sulphur content to best utilise the nitrogen being applied.
5 top tips for fertiliser applications to silage ground:
- To ensure nutrients are fully utilised, carry out soil analysis routinely to manage soil pH and optimise inputs for maximum yields.
- Alongside a qualified, advisor seek advice to develop a fertiliser plan for grazing and silage land.
- Apply fertiliser at the optimal time to achieve the best results for silage.
- Good soil management is required to optimise nutrient use and maximise grassland productivity.
- Visit www.fas.scot for more information.
Fiona Thomson, Senior Consultant and Area Manager, Fiona.Thomson@sac.co.uk
Posted by Unearthed News on 16/03/2026
