Accurate fertiliser application is critical to produce good yields and quality grass silage this season, according the Silage Advisory Centre.

Too much nitrogen will result in silage with high ammonia and butyric acid concentration, but too little will result in poor yields and crude protein content, explains IBER’s Dave Davies.

“It’s important farmers assess the quality of soils on their land before making fertiliser application decisions as nitrate-N levels in grass at harvest should be less than 0.02% of total nitrogen.”

Although 3-5 year soil testing regimes are recommended, when farmers are unable to achieve this, rough judgments can be made from previous land use and decisions made accordingly to achieve high quality 70D silage from first cut.

Decisions can be made as follows:

Grassland with more than 250kg N/ha applied last year:

• Soil N supply is likely to be high – application of 120kg N/ha suggested.

Grassland with 100-250kg N/ha applied last year or substantial clover content:

• Soil N supply is likely to be moderate – application of 120kg N/ha suggested.

Grassland with less than 100kg/N/ha applied last year:

• Soil N supply likely to be low, application of 150kg N/ha suggested.

“With spring grazing these amounts should be reduced by 25kg N/ha,” says Mr Davies.

” Farmers can also use the general ‘rule of thumb’ that in ideal weather conditions grassland will use 2.5kg N/ha/day to determine what is appropriate for different fields.

“However, there is no substitute for local knowledge and focus on the weather forecast when it comes to deciding on appropriate harvesting time,” he says.