Grow more grass by getting soil pH right

Tuesday 04 March 2014
Grow more grass by getting soil pH right

Since March 2013, EBLEX has held RDPE Skills meetings in upland areas in and around the North West. Last month they started a series of meetings aimed at spring and the lambing season (see Cumbria Events for meetings in Feb and March).

Below soil specialist Jim Bretherton (Agscope) touched upon a few key points at a meeting organised for farmers in Teesdale...

Get the basics right - calcium or mag lime?

Both calcium and magnesium alter soil pH for improved grass growth but each affects soil structure in different ways...

Key message: Test your soil for pH, magnesium and calcium and then use the right liming product.

Jim BrethertonJim Bretherton explained that soil acidity affects soil life and that this is the basic requirement for productive grassland - he said 5.8 pH was a realisitic target on dark peaty upland soils and 6.2 on loamy soils.

He said: "The most important point is if you need a mag lime or a calcium lime. Getting the right balance is key as it improves structure which opens up access to other minerals, just like getting the balance right in a dairy cow’s diet. A more detailed soil sample will give a mag / calcium index, standard soil tests don’t normally do this.

Calcium should always be the dominant mineral at a ratio of 4:1. P and K and sulphur also play a part.

"Some farmers have found the right type of lime can improve grass growth by 30% without any nitrogen needed."

calcium v manesium lime soilsHe also said too much of the wrong nitrogen (ammonium or sulphate), heavy rainfall and cropping can all reduce pH too.

pH, P and K for good structure

Soil from a health point of view is key – it is a living environment – there is as much living material in four to five inches underneath as there is ain an acre above.

Good structure affects yield, palatability. Soils that work well and are structured well will make a difference on drainage. Soils will warm up quicker if better structured.

Lime is important – on the hills it’s a concern, the west side of Cumbria particularly, as not liming the land as much has seen the water courses start to go acidic.

Like to apply lime little and often – try and use the right lime for your soil.

Get the basics of soil pH right.

Fylde coast: 35 inches of rain a year
Teeside: 70 inches average
Trough of Bowland: 112 inches last year

Nitrogen turns in to hydrogen which makes the soil more acidic by displacing calcium and magnesium.

If using ammonium nitrate think about using something else instead – i.e. calcium nitrate


Farmer questions and examples 

One farmer in the group tested soil this year from a field that he takes a crop of silage off every year. In 2007 it was tested at 6.6pH, which was too high, this year it was 5.5pH.

He said: "I don’t know if that’s the rain. It’s had one crop of silage off it each year and its not had excessive amounts of nitrogen on it but I was quite shocked.

"I had another field last year that had a similar result, I almost didn’t test it and that was 5.4pH. What do you suggest has had the biggest effect on it?"

Jim replied: "It could be the rain, could be nitrogen (both fields get a heavy dose of liquid nitrogen applied in the spring which is ammonium sulphate).

"On the scale of acidic elements, ammonium sulphate is right at the top, ammonium nitrate next, followed by urea in third

"One thing I use if soils are short of calcium, with pH going below 6, is CAN (Calcium ammonium nitrate) which is a nitrate with prilled lime. By putting calcium on you are counteracting the nitrogen all the time. The Australians are good at this as they work out each year how much lime they need to counteract nitrogen used."


When asked about liming fields under stewardship restrictions Jim said: "If you're working with Natural England guidelines to put on lime and looking for evidence to justify what you're doing then you should look at doing a mineral forage sample each year, checking how much calcium and magnesium has been removed in the crop.

"Natural England like soils at 5pH (for flower rich habitat ESAs) – dark soils are never going to get to 6. A realistic target is 5.5 to 5.6. A target for standard loamy, silts and clays is 5.8pH and above.  

"Calcified lime, bagged lime, is a good concept that you can put on yourself every year, every other year, to make a difference."

Those in the group that had tried this said they had seen a difference. Calcified seaweed was also praised. Jim said research in Wales had shown liming improved stocking density: "You don't necessarily need nitrogen to improve grass growth, you can do it with lime, p and k".

A few more liming answers...

Low soil pH?

You are low in calcium or magnesium. Most soils short of calcium will have a good level of magnesium but you don’t want too much of it. You need a balance of calcium and magnesium – too much magnesium produces tight soils that doesn’t allow air to get in.

Magnesium is important, but too much and it makes soils tighter, whereas calcium opens up the soil and is good for palatability and clover development. If you've not got enough calcium and you're trying to grow clover you’re going to struggle.

Best sort of calcium lime?

Calcium carbonate is the most reactive but prilled lime is good. The larger the particles the longer it takes to break down, the better the quality and whiter it is and powdered the better but it is more expensive.

Calcifert and Onya – The Agricultural Lime Association do a database of suppliers as lime does vary wherever you are in the country, but the most important point is if you need a magnesium lime or a calcium lime. If you're at 5.7, 5.8pH than prilled lime, little and often, would be enough to top it up.

Jim added: "Magnesium can make the soil sticky. Historically in and around the Ribble Valley for years we were scared of staggers whereby if too is put on and not enough taken off it builds up. Those that have swapped to calcium have found the top of the soils open up a bit and drain away a little better.


"Aerators are not always the cure to everyone’s ills but it can make a difference – some think it's better than a bag of nitrogen as it can get air in and soils will warm up quicker as air heats up sooner than solids."

Add a Comment

If you would like to leave a comment, please login or register for an account.