Field site 3: Harpenden, Hertfordshire

Find out more about how we're measuring greenhouse gas removal at our field site in Harpenden, Hertfordshire

A tractor for spreading receiving crushed basalt from a front-loader at our field site in Harpenden

At the Rothamsted facility in Harpenden, the demonstration plots closely replicate typical intensive arable crop farming environment and methods.

Enhanced rock weathering greenhouse gas removal (GGR) field trials will be conducted in 6 large demonstration plots (24 × 24 m each); 3 replicated treated and 3 controls. The soils are silt/silty clay loams, with a pH of around 6.6, and just 1% soil organic carbon (SOC), with plant-available silicon depleted by long-term intensive cropping, as is common in the UK. Treated plots will undergo annual crushed basalt topsoil spreading (40 tonnes per hectare) which will be ploughed in using standard agricultural equipment, with the control plots prepared the same way but without basalt.

How are we working on the Harpenden field site?

The arable rotation over the three year study will consist of nitrogen-fixing winter beans, winter wheat, and winter oilseed rape allowing us to test H4 with 3 crops contributing 55% of the UK arable cropped area. Each plot will be separated by at least 5 metres, in a near-flat 3 hectare field, and all cultivation and harvesting operations will be strictly limited to within each plot area to avoid between-plot soil movement during cultivations and ensure reliable mass balance assessment.

How are we measuring results of greenhouse gas removal and other co-benefits at Harpenden?

We will robustly measure GGR in years 1 to 3, and analyse potential co-benefits for crops and soils, and soil GHG fluxes by taking samples from each plot in a central area (5 metres inside each plot boundary) to avoid edge effects.

  • Soil samples will be taken in the 0-25 cm plough layer and subsoil depth (25–60 cm) every 6 months during the rotation (to establish a baseline and compare this with after treatment) to match the methods at Field Site 2 at North Wyke.
  • Soil pore water will be sampled during the winter season at 1 metre depth.
  • Co-benefits will be determined by measuring yields of grain and straw. A pathologist will also assess protection of crops from pest and diseases resulting from increased silicon uptake.
  • Soil GHG fluxes (carbon dioxide, nitrous oxide and methane) will be measured using static chambers over the 4 years of the rotation, just as we’re doing at our North Wyke field site.

Extensive prior data sets, continued measurements, and data from our Met Office site nearby (such as air and soil temperatures, soil moisture, rainfall) provide unrivalled long-term baseline data for assessing the effects arising from ERW.

Photo showing sunset over our field site at Harpenden