Expert asserts nitrogen supply critical to silage quality
4 May 2010 Assessing required levels of nitrogen (N) supply to growing crops is critical when aiming for high quality silage but its a delicate balance that only those farmers giving it serious attention will achieve.
Dr Dave Davies, silage expert with IBERS and the Silage Advisory Centre (SilAC), says accurate fertiliser application can have major implications on the quality and quantity of silage produced, and with increasing numbers of farmers relying on silage as a fodder management system, as much care as possible needs to be taken over its preparation.
Too much nitrogen supply will result in silage with high ammonia and butyric acid concentrations, explained Dr Davies. However, too little nitrogen will result in poor yields and crude protein content.
Nitrate-N levels in grass at harvest time should be below 0.02% of total nitrogen, meaning its important that farmers assess the quality of the different soils on their land before making fertilizer application decisions.
According to Dr Davies, although 3-5 year soil testing regimes are recommended, if farmers were unable to achieve this then rough judgments can be made from previous land use and decisions made accordingly in order to achieve high quality 70D silage from a first cut (which has a higher N requirement than a second cut, due to better growth conditions):
- grassland with over 250 kg N/ha last year: soil N supply likely to be high, application of 120 kg N/ha suggested.
- grassland with 100-250 kg N/ha last year or substantial clover content: soil N supply likely to be moderate, application of 120 kg N/ha suggested.
- grassland with less than 100 kg/N/ha last year: soil N supply likely to be low, application of 150 kg N/ha suggested.
With spring grazing the amounts should be reduced by 25 kg N/ha. Farmers can also use the general rule of thumb that in ideal weather conditions grassland will utilize 2.5 kg N/ha/day to determine what is appropriate for different fields. However, Dr Davies admits there is no substitute for local knowledge and focus on the weather forecast when it comes to deciding on appropriate harvesting time.
It is always better to harvest early when farmers know all the nitrogen has been utilized and the weather is set to be fine, he said. Its also far better to apply less than more fertilizer based on the local knowledge of the land and to harvest when the time is right rather than wait too long and end up with a wet two weeks!
More advice on planning for silage preparation, harvesting and use can be found at www.silageadvice.com, which provides farmers with down to earth, pragmatic advice and tools to maximize fodder and grassland management systems using baled silage effectively.
Farmers are welcomed to meet Dr Davies and other silage and forage experts at the Silage Advisory Centre stand at Scotgrass (Dumfries, 11th May) and Balmoral Show (Belfast, 12th-14th May).
Farmers visiting SilACs stand will also have the opportunity to enter a free prize draw competition to win free grassland health checks and reels of bale wrap film.
The Silage Advisory Centre is an industry initiative that promotes the science of silage to aid farmers decision-making on baled silage production, forage and grassland management. Its mission is to aid UK and Irish livestock farmers produce quality and nutritional silage at a reasonable profit through research, demo farms, seminars, knowledge transfer and advisory tools.