Maximising forage for the year

9th May 2019

Growing grass in Ireland is something that we as farmers do instinctively. Sometimes it is good to sit back and see the wood from the trees and think about the steps that are required to make truly great silage.

Agriland sat down with Ciaran Conway, Ruminant Nutritionist and David Hagan, Sustainable Agriculture Manger both from Devenish to discuss the steps to making great silage this summer.


Creating a silage plan

Knowing how much and what quality of silage you need is a good starting place for your annual silage plan.

For instance if you are a spring calving suckler herd, you will need silage for dry cows, milking cows, heifers, weanlings, and possibly finishing animals. While all these groups require good silage, certain groups like dry cows can be targeted with lower Dry Matter Digestibility (DMD) silage for their stage of production. The same will be true for dairy and beef finishing farms. Knowing your predicted stocking rate and land available are the first steps to maximise forage production. The table below outlines some of the parameters:


Dry matter intake (kg/day)

Dry Matter Digestibility % required

Suckler cows








Dairy cows*








Beef finishing




70- 74

<20 months


70- 74

*grass based system


At Devenish we have learned through our Soil Improvement Programme (SIP) that to grow great forages you need to know which nutrients your soil are lacking. When soil testing, the usual practice is to look at the phosphorus (P), potassium (K), pH and lime levels, however our experience at Devenish suggests that a much more comprehensive soil test which looks at the chemical, physical and biological aspects can give much better results.

Ciaran Conway explains: “When land is compacted, there is no air in the soil. This causes molybdenum to be in its reduced form where it is much more available for grass to take up, which it will. This will lead to higher molybdenum levels in silage, which could have a detrimental effect on animal health and fertility as it binds up copper.”


Nutrient maximisation

Once we know the fertility of the soil, we then need to know how many nutrients to apply. David Hagan explains: “Slurry is going to make up some of the fertiliser requirements, and testing slurry allows you to be specific in targeting the correct nutrients to help grow better silage while also reducing your fertiliser bill.

“This is important when it comes to potassium, knowing the exact amount will allow you produce silage that doesn’t have high potassium levels when feeding dry cows. There is a very delicate balance between the plant needs and the cow when fertilising with potassuim.”

David pointed out that a slurry inoculant like Digest It makes the nutrients in the slurry more available and the slurry easier to agitate and spread, resulting in less leaf contamination.

The recommendations from the Teagasc Green Book* shown in the table below, show that a lot of nutrition is needed for first cut silage. Silage can be hard on soil nutrients, it removes 4kg P and 25kg K per tonne of grass dry matter (DM), respectively. Sulphur is also very important as nitrogen and sulphur are the building blocks of protein and if you want high protein silage sulphur needs to be included. A good rule of thumb is to add one unit of sulphur for every 12 units of nitrogen, said David. For Nitrogen, another good rule of thumb is that grass will use 1one kg N (two units) per day. For first cut, you want to have your nitrogen out at least 50 days before you plan to cut.

Nutrient requirements for first cut silage.

Soil index






Kg/Ha (units/ac)

Kg/Ha (units/ac)

Kg/Ha (units/ac)

Kg/Ha (units/ac)


125kgN/Ha (100 units/ac) for first cut silage


60 (48)

40 (32)




185 (148)

155 (124)

125 (100)



15-20kgS/Ha (12-15 units/ac) in the spring



When to harvest

To make highly digestible silage with a high Dry Matter Digestibility (DMD), it should be cut just as the fourth leaf is fully out, DMD will fall as the fifth leaf appears and more so when grass heads out. For good quality silage you want your silage to analyse more than 70% DMD. The sugar and nitrogen content is very important - high sugars not only lead to higher energy, but also better preserved silage.

Ciaran added that testing nitrogen was important if there is too much nitrogen in the leaf, it buffers the pH reducing the sugar levels and may have a negative impact on silage fermentation.


Grass plant growth stages

Source: Teagasc Quality Grass Silage for Dairy and Beef Production Systems A Best Practice Guide


Harvesting the silage

The main issue with harvesting is to avoid soil contamination, this is generally down to incorrect setting of the mower and rake, therefore it is best to check your set up before harvesting to avoid any risk of contamination.

Wilting is a good way to increase the DM in the silage, Ciaran said the best way to get the get a good wilt is to use the conditioner on the mower and spread over the ground for 24 hours, weather permitting, then rake up and harvest.

Getting the silage into the clamp quickly is the next step in great silage production. The quicker you can get it into the clamp and sealed the more energy you will keep in your silage. However, compaction of the silage is key to drive air out and get a better fermentation. We should not under compact the silage in order to get it into the pit quicker. The best way to compact silage is to spread it out in nice thin layers of approximately six inches over the pit and continuously roll with the loader or tractor.

Sealing the pit is the last piece of the jigsaw. At least three layers should be used to seal the pit. Pay particular attention to the side walls and weigh down the entire surface of the plastic cover to keep air out.

This article primarily focused on grass. However, the same rules apply for most other forages. Devenish has a team of nutritionists and agronomists that can help you grow better forages and get more from your soil and slurry.

If you have questions about managing your silage quality, or would like to get involved in our Soil Improvement Programme, please contact Ciaran Conway on +353 8726 71202 or David Hagan on +353 8726 91119.

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