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Farm makes four soil management changes after carbon study

Michael Priestley 15 November 2022
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© MAG/Michael Priestley© MAG/Michael Priestley

A Scottish Borders farm has made four major farm management changes on the back of involvement in a soil carbon study funded by the Scottish government.

Jamie Cairns runs South Riccalton, a large upland farm near Jedburgh, and rents a smaller arable unit, Netherwells, from his brother.

Netherwells provides straw for the cattle at South Riccalton, which are typically housed after Christmas until calving, and South Riccalton is now returning organic matter and soil fertility by taking sheep down for wintering.

See also: Blackgrass down and wheat yields up after integrating sheep

Jamie Cairns with cows

Jamie Cairns © MAG/Michael Priestley

Farm facts: South Riccalton Farm

  • Main farm is 560ha (1,383 acres)
  • 40% rough grazing, one-third permanent grass and remainder temporary leys
  • Rents in 60ha (150 acres)
  • 180 suckler cows bulled this year
  • 1,100 ewes and 350 hoggs

Why get involved?

  • Soil health was a gap in Mr Cairns’ knowledge, so he took the opportunity to learn
  • Nitrogen use efficiency, carbon audits and output calculations seem like the direction of travel for the industry, so it is best to get in early
  • Costs are rising and expansion plans are on hold. The plan now is to cut back on fertiliser and bought-in feed, cull hard, and slowly increase stocking rates in a less input-heavy system

What the study showed

Mr Cairns learned his farm is reasonably productive, but bagged nitrogen has the potential to be the real villain for nitrogen use efficiency if not used optimally.

He had been adding 400-500t of calcium lime a year and was doing regular soil sampling to manage pH and indices, and the project proved the value of this effort.

Soil and nitrogen performance in 2020-21

  • 9t of nitrogen applied at 14kg N/ha
  • A further 13kg N/ha imported in the form of high-energy concentrates, which was 22.4t higher (total of 124.3t) than normal due to late spring in 2020
  • 469kg/ha of liveweight produced adjusted for forage hectares
  • Nitrogen use efficiency of 25% (at the high end for a livestock farm)

Mr Cairns says: “Aiming for 1,000kg liveweight/ha might be reasonable for some, but we are at 1,000ft here, so targeting 600-700kg might be more sensible. 

“Increased output must be done in a cost-effective way because, if there is no margin, there is no point.”

Soil carbon results at South Riccalton

Field

Comment

Loss on ignition (%)

Bulk density (%)

Carbon (t/ha)

“Good” in-bye silage field and formerly barley

Ploughed three times in past 15 years

9.2

6.1

105*

“Poor” in-bye field needing a reseed

Ploughed once in 20 years

6.93

5.9

109

*The soil carbon benchmarks set by the study suggested low was less than 60t/ha, moderate was 60-120t/ha, and high was more than 120t/ha, although no official grassland benchmarks for Scottish grassland soils exist

Changes brought in because of the study  

1. Keep living roots in the ground over winter

  • How? On top of the usual practice of putting in hybrid kale via min-till to finish lambs, a further 28ha (70 acres) of grazeable cover crops have been put in after spring barley to graze with ewes before lambing. Both kale and cover crops after spring barley will be ploughed out and put into spring barley. 
  • Why? This will provide a finishing crop for 600-700 lambs and could be a way to cut ewe roll costs by wintering some ewes. Min-till and cover crops mean living roots are kept in the ground longer, so soil biology stays alive and carbon remains in the soil.

2. Monitor loss on ignition when soil testing

  • How? This is added on to the standard soil test the farm was already doing and is being funded (up to £30/ha) by a Scottish government grant for arable/improved grassland. To qualify, the pH, potassium, phosphorous and loss on ignition must be tested in each field.
  • Why? Loss on ignition measures soil organic matter, which is known to be key for soil biology and drought resistance, and can relate to soil carbon.

3. Soil test different parts of fields rather than simply at field level

  • How? Assess field topography and if the field as an obvious feature, such as a slope or a valley, take a sample in the distinct parts of the field.
  • Why? Huge in-field variability was shown in the study. One field measured 7.04mg/litre for phosphate and 120mg/litre for potassium, but ranged  from 1.9-16.5mg/litre and 81-336mg/litre, respectively, when divided and sampled in six parts. Some money may be saved by sampling a field in two or three obvious areas and treating them differently with the spreader.

4. Regenerating pastures to reduce bought-in nitrogen

  • How? Clover was stitched into an 8ha (20-acre) field in early June. The dry conditions meant a drill proved a good option, but Mr Cairns says he would like to use an air seeder in the future. A few Scotch thistles will be controlled by spot-spraying. Balansa clover, a vigorous annual, was used as a one-hit wonder and will be followed by a more persistent white clover, which will be stitched in next year.
  • Why? This will fix atmospheric nitrogen. The field typically uses 2t of a 16:16:16 product, while this year it produced a great crop of grass with just clover. This saved £1,500, based on a fertiliser price of £750/t.
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