Fertiliser requirements for first cut of silage
WHILE some farmers might say the only silage they are concerned about at the moment is the silage the animals are eating or sitting in the yard, we are at the time of the year again when fertiliser for early first-cut silage will need to be spread.
Looking at the medium-term forecast, there should be a good opportunity to spread in the coming week with ground conditions hopefully drying up.
It should be noted that, on a lot of farms, fertiliser for grazing is only now starting to go out as well.
It’s very important to get this spread now so that you will have enough grass to get stock out when the weather and ground conditions allow.
There has been very little grazing done on silage ground this spring so getting fertiliser spread and silage cut early will probably be the best option in most cases as it is now too late to start grazing if you want to cut in late May/early June. Grass covers on silage ground are going to be good where fields were closed up in early autumn.
Grass silage has a large nutrient demand, and adequate Nitrogen (N), Phosphorus (P) and Potassium (K) are essential for maximising grass/silage yield.
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.
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 re-seeded swards (0-3 years) will have 25 per cent higher N demand.
A crop of grass silage (5t/ha of DM) will require 125 kg N/ha (100 units/acre). Grass silage will take up, on average, 2.5kg/ ha/day of N (two units/day). Therefore, apply N at least 50 days before cutting to ensure full 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 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.
Consult the most recent (three to five years) soil test reports to determine the P and K requirements (in organic manure and fertiliser) for silage fields.
A crop of grass silage will remove approximately four kg of P and 25kg K/tonne of grass DM.
Organic manures are an effective source of N, P and K and can provide a large proportion of crop P and K requirements at relatively low cost.
As a simple rule of thumb, you can assume that for every 1,000 gallons of cattle slurry you spread, the nutrient content of that slurry will be approximately six units of N, five units of P and 30 units of K. For example 3,000 gallons/ ac of good quality cattle slurry (seven per cent DM) will supply sufficient P and K levels to grow a crop of grass silage.
The maximum amount of Potassium (K) that you should be applying should be 90 units/ acre.
As a general guide on Index 3 soils, the nutrient requirements for a good first cut of silage will be approximately 80 to 100 units of N/acre; 16 units P/acre and 90 units of K/ acre, which can be supplied by a combination of organic and chemical fertiliser.
It’s important to refer back to your most recent soil sample results and also to your nutrient management plan to ensure maximum return from fertiliser as well as adhering to the legal limits for both N and P fertilisers.
In light of the current COVID-19 situation getting the fertiliser out is another way of social distancing yourself from others.
Where you still have to order fertiliser get this done over the phone and where deliveries are being made allow drivers to do their work remotely.