Fertilising for first cut of silage
With the recent spell of dry weather and increased growth rates, conditions have been ideal for grazing off silage ground and getting ready to apply fertiliser.
Two common questions that are often asked in relation to first-cut silage are: should I graze off the silage ground first before I apply fertiliser; and what fertiliser should I apply?
The answers to both questions will be farm-specific and will be dependent on a number of variables such as grazing management in the autumn/spring period; ground conditions; grass cover; and soil fertility. Grass silage has a large nutrient demand, and adequate Nitrogen, Phosphorus and Potassium is essential for maximising grass yield and producing sufficient winter feed.
Maintaining soil pH at 6.3 to 6.5 for optimum grass production is also essential to maximise the availability of soil N, P and K that is applied as either organic manure or artificial fertiliser. Nitrogen (N) is the key driver of grass silage yield. Grass swards with high levels of perennial rye grass will use N more efficiently than older swards.
Recently reseeded swards (zero to three years) will have 25pc higher N demand. A crop of grass silage (5t/ha of dry matter) will require 125kg N/ha (100 units/acre).
Grass silage will take up on average 2.5kg/ha/day of N (2units/day); therefore, apply N at least 50 days before cutting to ensure full N utilisation.
Make adjustment for fertiliser N applied for early grazing. For example, assume ~25 per cent of early N applied will be available for the silage crop.
For example, where 40 units/ac of N is applied for grazing, reduce N applied by 10units/ac for grass silage crop. Phosphorus (P) and Potassium (K) are essential to maximise grass silage yields; therefore, adequate supply of these nutrients in the soil is critical.