In 2013, Lakeland Dairies, along with the Belfast-based nutritional products and solutions provider Devenish Nutrition, and UK dairy nutrition specialists, Thomson and Joseph, set up a soil improvement programme across three monitor farms in the Lakeland Dairies catchment area.

With the first three years of the programme completed, now is a good time to evaluate what can be achieved when there is a renewed focus on the soil. At present, it is probably the case that we understand more about what is happening in the two miles above our heads than in the first few inches below our feet.

In the three years that he has been involved in the programme, Clive Reed who farms just across the border in Monaghan has improved grass utilisation on his grazing platform from 7.8t dry matter per hectare (DM/ha) to 9.4t DM/ha. He has also improved milk from forage, with 3,585 litres produced in 2013 compared with 3,884 litres produced in 2015. The increases realised are all down to improvements in management – no extra fertiliser has been applied over the period.

According to Alan Hurst from Lakeland Agri, the soil improvement programme has encouraged farmers to make the best use of the resources available to them, which in turn will increase efficiency, profitability and promote sustainability.

With recent figures from AFBI suggesting that the average dairy farm in NI utilises around 7.5t DM/ha, and the average beef and sheep farm only 4.1t DM/ha, there is considerable scope for improvement. No doubt, better grazing management is the main starting point for anyone looking to improve these figures, but beyond that the next stage is to consider the soil.

“Grass is our cheapest form of nutrient. It is key to profitability on livestock farms, and the figures from AFBI show that there is massive potential for improvement. It should also be remembered that grass is the unique selling point for agriculture across the island,” said Gill Gallagher from Devenish Nutrition.

The soil improvement programme has split management into three steps:

Step one: Physical

With recent studies suggesting that poor soil structure will lead to up to a 40% reduction in grass growth, the first step in the programme was to alleviate the negative effect of soil compaction.

Poor soil structure reduces yield because grass roots are less able to penetrate into the soil. There is also a reduced response to fertiliser and less biological activity in the soil, which leads to poorer cycling of soil nutrients. Ryegrass is less able to dominate, so weed grasses take over which means lower quality herbage for livestock.

The main causes of compaction in grassland are machinery and livestock. The best advice is to keep machinery off wet fields and, where possible, to use machines with larger tyres and reduced inflation pressures. Overwintering livestock in fields or grazing low plant density forage crops late in the season significantly increases the risks.

To assess whether there is compaction issue to be addressed, the starting point is to dig a hole with a spade. According to Gill Gallagher, a non-compacted soil will have vertical cracks, good earthworm activity, should crumble easily and with grass roots penetrating up to 30cm. A compacted soil will be blocky, with horizontal cracks and the grass will have a shallow root structure. It will often have a stale smell as there is no air getting into the soil to break down organic matter and manures.

Molybdenum

One indicator of an increasing problem with soil compaction is the increased levels of molybdenum levels being found in grass silage. In well aerated soils, molybdenum is oxidised which renders it insoluble, thereby making it difficult for plants to absorb through the roots.

Once air is excluded, it becomes more available to the grass plant. High levels of molybdenum can affect cow fertility due to its ability to tie up rumen copper, which is linked to reduced oestrus cycling and infertility.

On the Reed farm, molybdenum levels in silage have been reduced by 51% which Clive believes has contributed to improved fertility within his dairy herd.

To help alleviate soil compaction, he uses a soil aerator. “I did try a subsoiler but it pulled up a lot of stones. On this farm, the aerator works well, but it is important to only use it when ground is reasonably dry or you just end up smearing the surface,” he said.

He has also ploughed and reseeded much of his grassland block over the last five years, which will help to solve any issues with surface compaction. However, it should be noted that when reseeding there is inevitably multiple runs over the field with machinery, which can cause compaction, especially if the ground has been power harrowed. “We have seen situations where soil is compacted even in a new reseed. It is not always the long-term solution,” advised Gill Gallagher.

Step two: Chemical

The second step in the soil improvement programme is to undertake regular analysis to identify and correct any nutrient deficiencies and imbalances in the soil. The first action should always be to correct soil pH below 6, or phosphorus or potassium indexes below 2.

But beyond that, farmers in the programme have also been encouraged to look at the calcium to magnesium balance in their soil. Studies have shown that where magnesium is too high, it can impede the availability and uptake of other soil nutrients. Also, the addition of calcium can actually act to improve soil structure and drainage.

On the Reed farm, the soils are generally high in magnesium, so he has applied gypsum to help improve the balance between calcium and magnesium. The alternative is to source and use calcium-based limestone when correcting low soil pH.

“The opposite can also be the case, and some farms with soils low in magnesium should be using magnesium-based lime,” said Gill Gallagher.

Step three: Biological

The final step in the soil improvement programme has been to use an additive in slurry to improve the nutrient availability and reduce ammonia losses.

The product used is Digest-it, a liquid biological composting product which contains aerobic bacteria, enzymes and nutrients, and designed to aerobically digest slurry. It is manufactured by Australian company BioAg and imported into Britain and Ireland by Thomson and Joseph, for distribution via Devenish and Lakeland. A total of 20 litres of product treats 100,000 gallons of slurry and costs around £200 plus VAT.

Trials at the Devenish research farm in Dowth, Co Meath, suggest that there is a payback of 3:1 when using the product. When evaluated on pig slurry, treated slurry resulted in a 36% increase in grass dry matter yield, when compared with untreated slurry. In a trial using dairy cattle slurry, the yield benefit was 23%.

The response is mainly due to the product breaking down the ammonia in slurry into microbial nitrogen, which is a more long-term source of nitrogen to the plant.

Farmers who use the product also maintain that there is less smell (due to reduced ammonia) and the slurry is easier to mix.