Farm Ireland

Tuesday 20 March 2018

Explosive grass growth rates of up to 150kg alter the landscape overnight

John Donsworth

IF there is such a thing as pent-up emotion in grass growth, then it was all released in the last 10 days. Grass growth rates have gone from an average of 50kg DM/ha to 120kg DM/ha in a matter of a week. Dairy farmers that walk their farms regularly have quoted growth rates as high as 150kg over a four day period.

That type of growth rate will change the landscape overnight.

Nitrogen fertiliser has underperformed over the past six weeks. It grew a certain volume of grass, but nowhere near the amount expected.

The weather conditions just didn't allow any growth worth talking about to take place.

However, fertiliser has a life cycle of six weeks once it is applied. Once soil and air temperature reached the levels of last week, a serious amount of this nitrogen was all released at once, with the result that we had an explosion in grass growth rates.

While all this growth is indeed a blessing, it doesn't come without its problems. Some of the grass I saw last week should have been accompanied by a health warning for the cow. Despite the poor May, cows have performed very well, with milk protein percent holding up remarkably well.


However, we are now into what I call the silly season for grass quality. The June milk protein percentage is generally the poorest of the 12 months and this can only be because of the grass quality offered to the cow.

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What must you do to avoid having cows inside in paddocks that are all but meadows? Firstly, walk the grazing block.

Sounds simple, but how many of you do it? 95pc of grazing blocks can be walked in an hour. Believe me, you will be surprised how much of the green stuff you have. I walk farms regularly, usually in preparation for discussion groups.

At the end of virtually every walk, the farmer will either say "I didn't think I had so much grass" or "I have less grass than I thought".

Why is the farm only walked when the discussion group is coming? Only the really strong, committed group members will have grass covers for you on the day of the walk.

The guys who don't have the figures will use words like "plenty" to describe what is on the grazing block. That's about as useful as an ashtray on a motorbike.

While we all agree that simply walking the farm is a very good idea, what actions are taken as a result is an entirely different matter. Without crunching any numbers, some farmers will move the cows to what they consider the next available best quality grass.

This may mean skipping the next two grazing paddocks. In the majority of cases, this is the correct decision.

But what if you are able to put figures on what you found? Would you make a better decision that will leave you with more profit?

Putting figures on your walk means arriving at a figure for grass cover, establishing the current stocking rate, and then dividing the average grass cover figure by the stocking rate.

This will give you the grass cover per cow. This is a very valuable figure to have, as it will give you greater confidence in your decision making.

It will also allow you to adopt an aggressive approach to your current grass supply situation.

You can take this a stage further by putting your figures into a computer and come up with a grass wedge (see graph).

A grass wedge is simply a visual picture of the volume of grass on the farm. Each paddock is represented as a bar graph and the paddocks are above or below an imaginary trend line.

This line is important. It is arrived at by multiplying the stocking rate by the cow's grass intake (usually 18kgs) and then multiplying the result by the rotation length.

In an ideal world all the paddocks would be just up to the line. But as we all know, what's happening at the moment is not the norm, so several of the paddocks are often above the line, as is the case with the example farm used here.


The cover per cow tells us all we need to know. It is at 280kg/cow. That's a grand total of 15 days grass ahead of the cows.

This figure proves that it is time to bite the bullet. What paddocks will you step over? I would immediately take out the best four paddocks on the farm i.e. 11, 13, 17 and 12.

That means the cows are now going into paddock 14 which has a cover of 1700. The cover per cow is now down to 198 (11 days of grass).

The current stocking rate of 3.8lu/ha now moves to 4.65lu/ha. A growth rate of 80kg/day is required to keep the new situation afloat. I don't consider that a problem.

The rotation length on this farm is 27 days. Removing the paddocks suggested will bring that back to about 20 days.

Currently, one could operate at a cover per cow of 120 kg. That's only seven days grass ahead.

Ideally, cows need to be going into paddocks that have grass covers of between 1300 to 1500kgs of dry matter. That's 4-5 inches of grass. The benefits are no topping, quicker recovery and high leaf content.

John Donworth is a Teagasc dairy specialist based in Limerick

Indo Farming