Soil sampling and wave mapping bring low cost grass growth

Electromagnetic wave mapping and intensive soil sampling at a Welsh dairy farm are driving grassland production at a lower cost.

Precision technology is routinely used on arable farms, but dairy farmers such as Nigel and Chris James are realising the advantages it also offers in managing nutrient inputs.

The brothers were prompted to scrutinise the application of nutrients at Stackpole Home Farm, near Pembroke, following the farm’s inclusion in a catchment sensitive area and nitrate vulnerable zone (NVZ).

They run 1,100 dairy cows and 360 followers on 480ha of free-draining limestone and shallower red sandstone.

The herd is predominately New Zealand-bred Friesian with an average milk yield of 5,000 litres at 4.3% butterfat and 3.65% protein.

Fields are reseeded every 10 years using late-heading perennial varieties.

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Last year, the James’ commissioned external contractors to undertake conductivity testing and intensive soil sampling in every field, covering the whole farm.

The service cost £22/ha and will be repeated every three years. “Each field was sampled multiple times rather than the customary once,” Chris explains.

The technology features an instrument towed behind a quad bike that sends and receives electromagnetic signals and measures the amount of resistance – which varies from gravels to heavier soils.

This information is transferred to contour maps and these, together with the soil sample results, reveal the fluctuating nutrient and pH levels in each field.

Chris James says precision technology shows clear evidence of past grassland management

“We were surprised at how nutrient levels varied between fields and in fields. There was no commonality between pH, phosphate and potash,” says Chris.

In a single field the indices ranged from a pH of 5 to 6 and a potash of 0 to 2.5.

Some fields showed clear evidence of past management – in particular, one field used for buffer feeding silage to cows during a dry spell.

“You could see the evidence of this right up to the line where no silage was fed: the phosphate levels were very high where the cows had been feeding,” explains Chris.

But in other fields the variations are simply the result of different rock strata and soil types.

Benefits of measuring

In the past, lime, potash and phosphate were spread at a uniform rate across the farm but the mapping system is now used as a guide to apply nutrients only where they are needed.

“We have cut down on the volume of nutrients in areas that didn’t need them. We are pinpointing the application rate rather than doing a blanket spread.

“By using this system we will get the whole farm growing grass at an optimum level,” adds Chris.

Nutrient application

An equation is used to calculate what levels of nutrients to apply in subsequent years to maintain indices.

This spring, 200t of lime were applied at a variable rate to address the areas with a low pH. This represented an investment of £29/t.

Data from electromagnetic mapping is sent to the software running on the variable-rate spreader. “Application rates across the farm varied from none at all to 9t/ha,” says Chris.

Slurry was applied to the outlying fields where shortfalls in phosphates were evident. “One of the easiest things for us to do was to drive more slurry to the fields furthest away from the slurry pit.

“In the past we would have been guilty of hauling the slurry to the closest fields only,” Chris admits.

When the NVZ designation was made in 2008, the capacity of the farm’s slurry store was increased; this allows slurry to be used more productively.

The 9,000cu m store can hold slurry generated over five months. This slurry is tested for its nutrient value and a standard value is used.

The application rate is estimated. Precision technology is also being applied to nitrogen use.

The farm’s fertiliser spreader has been upgraded to a variable-rate model with a hydraulic drive. The machine uses GPS to map the boundary and memorises this information.

The grazing platform is split into 4ha paddocks; an auto shut-off feature on the spreader means there is less waste.

The machine has load cells and measures the output rate so the application rate is constantly monitored, allowing the desired rate to be applied at any tractor speed.

“Nitrogen isn’t retained in the soil, which means you apply only what the crop needs, but we want an even crop across the field.

“This technology allows us to achieve this,” says Mr Chris, who uses straight nitrogen, potash and phosphate.

Grass production is being monitored to ensure the system is making a return on the investment.

Platemeter

Farm manager Gethin Brown measures grass growth weekly using a quad bike-mounted platemeter. “That information allows us to compare ourselves with other similar sites,” he says.

“Our aim is not to increase production but to maintain it, using fewer nutrients that we would otherwise have applied.”

Knowing how soils are going to respond and react to inputs means benefits for the environment, too, he adds.

“We are using our nutrients more effectively. We are targeting the fields that have low indices with our own slurries and farmyard manures.”

Mr Brown doesn’t envisage precision technology will facilitate higher grass yields, but he expects a far higher use of nutrients.

“This will mean cost savings to us and it reduces the environmental impact of our farming practices.

“We are not enriching the soil that is already up to standard but using our inputs more prudently. We can now target these based on informed decisions.”

The benefits of precision technology can be enjoyed by all farms, regardless of size. “A small farm can gain as much benefit if they contract in the equipment,” says Chris.  

However, Chris concedes there is still one crucial element he cannot regulate. “What really drives our grass growth is rain. “We can fine-tune our nutrient applications but it is moisture levels that can make or break our grass production in a season.”