Mileage in Silage Wk. 12

Mileage in Silage

Winter performance and costs for housed livestock are driven by the quality of silage fed.

There are many things we can control to improve silage quality: soil nutrients, ley quality, shutting and cutting dates, animal manures, harvesting and ensiling methods, storage and feed out.  Grass quality at cutting is key to producing high quality, well fermented and stable silage.

This twelfth Mileage in Silage bulletin gives results for a second cut sample from Tudur Jones dairy and sheep farm Tyn Rhos, Betws y Coed.  Tudur plans to take a second cut in around 2 weeks.

Tyn Rhos, Betws y Coed: GDC IBERS ‘GRASS FOR SILAGE TEST’ RESULTS (26 July 2012)

This week’s sample is from a long term ley shut up for a second cut.  First cut was snatched just over 3 weeks ago and a split dressing of fertiliser was applied: nitrogen at 62 kg/ ha (50 units /acre) as soon after cutting as weather and ground conditions allowed followed by a further 31kg /ha ( 25 units /acre ) early last week.  Phosphate and potash was also supplied to meet crop needs.  With the cold wet weather, low soil temperatures and low light intensity initial regrowth was slow but it has taken off with the recent sunshine and warmth.  The sample shows good energy level, and “D” value and moisture content consistent with young leafy regrowth.  The high protein and Nitrate N % reflect crop uptake of the recent nitrogen application.

The simple rule is that grass will use an average of 2 units N/acre/day (2.5KgN/ha/day).  Next week’s grass sample will show how these have changed and will indicate if the nitrate N % is on target for cutting.

Nitrogen has a very large effect on the yield of ryegrass grass swards if soil structure, pH, water, temperature and other nutrients are not limiting.  Research indicates a grass growth response of up to 10 kg DM per kg of N applied in late summer under good conditions, so at current N fertiliser prices grass is a cheaper option than silage and compound feeds.

Effect of fertiliser N price and grass growth rate (kg Dry Matter) on cost of summer grass (p/kg)

At £300/t for ammonium nitrate (34.5%N) a kg of N costs 87p

For full details on nitrogen recommendations for grass, see The Fertiliser Manual (RB209)Defra

http://www.defra.gov.uk/publications/2011/03/25/fertiliser-manual-rb209/

Topical Tips

The hot dry weather in many parts of Wales last week led to frenetic grass cutting as farmers who had been waiting to harvest for many weeks were able to get crops in.  Generally wilting grass helps improve silage fermentation, reduces effluent losses and transport and storage costs.  However it is possible to ‘over wilt’ in high temperatures, strong winds or mature grass which becomes too dry and reduces nutritional value because of respiration losses, makes consolidation difficult and increases the risk of secondary fermentation at feed out.  Sun and wind can double the rate of wilting compared to a still overcast day.

Target Dry Matter (DM): Grass for Silage  

• Clamp : 25- 30% DM   
• Bale: 30-40% DM 

How to estimate grass dry matter levels

The squeeze test can be used to estimate the dry matter percentage of fresh grass.  Take a representative sample of grass and cut it into 2 - 3 cm lengths, roll it into a ball about twice the size of a golf ball and squeeze it in your fist for 30 seconds.  Approximate dry matter percentages are shown in the table below.

Grass dry matter levels

If grass in the field is drying quickly and it can’t be ensiled/baled straight away, row up to help slow down wilting.

If grass is too dry to consolidate easily in the clamp a layer of freshly cut grass on top may help improve consolidation and lower the overall dry matter.

Recommended Chop Length for Different Forage Dry Matter Content

To help consolidation and reduce oxygen levels when ensiling dry grass, monitor the dry matter and alter the chop length; the higher the dry matter the shorter the chop length needed.