2.1.7 Part 3: Temperate Grassland Agricultural Impacts

How much Soil Organic Carbon (SOC) was held in virgin North American Prairie soils prior to conversion?

Between 100 and 200 tonnes of carbon per hectare, accumulated over thousands of years under deep-rooted perennial grasses.

How does ploughing/tillage reduce carbon stores in grassland soils?

Ploughing disrupts soil structure, exposes buried organic matter to oxygen, and accelerates microbial decomposition, releasing stored carbon as CO₂.

What proportion of Soil Organic Carbon (SOC) is lost when natural grasslands are converted to cropland?

Agricultural conversion causes a 30–50% loss of original SOC, equivalent to a loss of 20–60 tonnes of carbon per hectare.

Why do annual crops (e.g., wheat, maize, soy) fail to build soil carbon like natural prairie grasses?

Annual crops have shallow root systems and short growth cycles, returning significantly less organic matter to the soil each year compared to deep-rooted perennial grasses (which root 1–2 metres deep).

What climate feedback risks exist for agricultural soils in temperate grasslands?

Higher temperatures accelerate microbial soil respiration, while increased drought stress reduces plant productivity, risking further declines in soil carbon storage.