Planning for a crop of second cut silage

Over the next few weeks 1st cut silage will begin. This is also an important time to think about the nutrient requirements to support 2nd cut silage later in the season. Where a crop of 1st cut silage has been harvested is it vital to get nutrients applied for the new regrowth. 2nd cut silage crops will generally be lighter that a 1st cut ranging from typically 2.5-3t DM/ha versus approximately 5t DM/ha for a 1st cut.

Nutrient Applications

To maximise a crop of 2^nd cut silage a balanced nutrient supply is essential, with adequate Phosphorus (P) and Potash (K) applications.

Nitrogen will drive grass growth and yield and it is important to get N applications right to support the crop growth whilst also ensuring you are only applying what is required by the crop. Newly reseeded swards with a high ryegrass content have to potential to utilise the applied N more efficiently.

P and K recommendations should be based on recent soil test results. Fields that are regularly cut for silage will have a significant requirement for P and K due to the high removal of these nutrients by the crop. It is vital that what is removed is replaced.

Utilising Slurry 

Potash is particularly important to support crop yields and where slurry is available it should be prioritised on the silage ground to replenish the K removed. 1000 gals of good quality slurry (7% DM) will provide approx. 6 units of N, 5 units of P and 30 units of K. Take care not to apply if weather is to dry and avoid applying too thick as it could smother the grass plants. Where slurry and chemical fertiliser are being applied allow a week apart between applications.

As per the nitrates regulations, all derogation farms must apply 100% of their slurry using low emission techniques. For anyone at 170kg/N/Ha and exporting slurry, where slurry is applied after the 15^th of April it must be applied using LESS technology. Low emission spreading will increase N utilisation whilst also improving air quality. LESS will also reduce grass contamination which means slurry can be applied when re-growth is occurring and the sward is actively growing.

Remember, where slurry has been applied take into consideration the nutrients applied and reduce chemical applications accordingly.

Key Considerations

Lime: Consideration should now be given to lime applications once the 1^st cut has been harvested, it is not necessary to leave applications to later in the season. Ideally we want a soil pH of 6.3 and where soil analysis indicated lime is required we shouldn’t delay in these applications. Correcting the soil pH will allow applied nutrients to be more available to the crop whilst improving soil structure and increases persistency of ryegrass and clover. Where slurry has been applied leave a period of a week before applying lime or alternatively when lime has been applied avoid slurry application for three months. If urea has been applied allow a period of 10 days before applying lime or a period of three months where lime has been applied before urea. This is usually not required when applying CAN or Protected Urea’s.

Weather Conditions: As always, before applying slurry or chemical fertiliser ensure suitable weather conditions with no heavy rain forecast for 48 hours. Ensure adequate buffers are maintained when applying close to any waterbody, 5m should be maintained for slurry and 2m for chemical fertiliser. Consider a slit application where conditions are less favourable, in particular on light, free draining soils that are at a higher risk of leaching.

Sulphur: Closely related to nitrogen use efficiency and applications are required for a crop of 2^nd cut silage, applying Sulphur will also help Improve grass DM yields as well as quality.  

GAIN Momentum Programme

The GAIN momentum programme, as outlined in the table below recommends these application rates to support a crop of 2^nd cut silage at a soil index level of 3 for P and K and assuming that all the required P and K was applied for the 1^st cut.

First Published: 18 May 2021