Things to think about for silage after the spring of 2018

Published 18 May 18

Silage StoryGenerally grass growth has been lower this spring due to the cold and wet conditions, although recovery has happened after some nicer spells of weather. For grass, heading dates are ‘programmed’ into the plants based on day length and temperature so it is unlikely that the recent weather will greatly affect the time of heading, but may affect yield. 

Yield and quality will be affected by when the field was last grazed (see Table 1). It is likely that on many farms, silage ground has been grazed as grass was short early in the season.

Table 1. Estimates of effects on silage yield and quality

Last grazing

Silage yield reduction


Impact on quality


1 March



15 March



28 March



10 April



Reference: AS Laidlaw and CS Mayne Setting management limits for the production and utilisation of herbage for out-of-season grazing; Grass and Forage Science, Volume 55, pp14-25 (2000). 

Soil concerns

It was common this spring to be grazing in wet conditions which has implications for soil structure. Fields need to be monitored this season to see if any need remedial action in the autumn. Yields could also be affected by the late grazing and impact of damaged soil structure. Work from Ireland has shown that heavy poaching in the spring will reduce total production by 40 per cent.

Soil contamination is a concern if ground conditions stay wet. It could be baling is an option as there will be fewer, lighter movements of vehicles compared to clamping.  Acid inoculants could be considered as they help to minimise spoilage caused by contamination.



Grassland can utilise 2.5kg N/ha/day (around two units of N/acre/day) under ideal weather conditions. This can come from soil N, manures and inorganic fertiliser. Applications may not have happened due to ground conditions, or if applications did happen then nitrogen uptake could have been reduced due to the weather. It is worth thinking about the days since the application, the amount and the growth that has occurred. The impact of nitrogen not being fully utilised by the crop is higher than ideal ammonia-N levels in the silage analysis.

The AHDB Nutrient Management Guide (RB209) provides recommendations on nitrogen applications for grass silage (see Table 1). 

More details is available here

There is a risk that the appropriate applications of phosphate and potash were not applied due to the ground condition or risk to animal health if grazing was still happening. There is limited benefit applying these nutrients so close to cutting. Talk to your FACTS adviser and update your nutrient management plan as it could be that applications are higher for later cuts or adjusted for offtakes. The phosphate and potash recommendations for grass silage are in Table 2.

Sulphur is highly water soluble so it is very likely that soils are short of sulphur, especially as you move into second cuts.

Analysis of uncontaminated herbage sampled just before cutting is a useful indicator of deficiency. Tests can be arranged via your local merchant. The information can be used to assess the need for sulphur for future cuts. The critical level is 0.25 per cent total sulphur or an N:S ratio greater than 13:1.

For silage cuts, the recommendation is 40kg of SO3/ha before each cut. Organic materials can be a good source of sulphur, so it doesn’t all need to come from a bag.

More information can be found here:

Reducing waste in the silage clamp

BRP manual Making Grass Silage for Better Returns

Improving silage making webinar