Earthworm Engineers #3 – Organic vs Conventional Systems

5184 3456 Sectormentor for Soils

Welcome to the third instalment in our Earthworm Engineers series where you can learn from some of the best science about the value of these amazing creatures. We’re so excited that Professor Jenni Dungait is now the editor of the European Journal of Soil Science – and she’s made some important earthworm papers open access for a month. We’ve picked our favourite four and summarised them in this blog series.

Access the earthworm archives in the European Journal of Soil Science, to learn more about the science behind on-farm worms!


#3: The impact of soil carbon management on soil macropore structure: a comparison of two apple orchard systems in New Zealand

This study compares two sites of the same soil type under apple orchards on one farm. One site had been under organic treatment, with regular compost application and grass cover, while the other was under ‘conventional’ treatment, with regular irrigation, fertilisation and herbicide applications.

When testing for earthworm populations, the researchers consistently found more earthworms in the organic soil compared with the conventional soil. They also reconstructed the 3D ‘macroporosity’ structure of both soils using X-rays, and again found greater macroporosity within the organic soil compared to the conventional soil. This isn’t a coincidence! Macroporosity is defined as the network of pores with a diameter of over 0.3 mm in the soil, and earthworms are known to create these kinds of channels.

This increased macroporosity is important for several reasons. First, it is known to increase the rate that CO2 in the atmosphere is locked up as soil organic carbon (SOC), which both increases soil fertility and also has potential to reduce the rate of climate change. As expected, this study then found that the organic orchard had a 32% greater SOC content than the conventional soils! Increased macroporosity also improves the soil structure, as the stability of soil aggregates is increased, which allows more microbes to live in the soil.  

Denitrification rates are known to increase in anoxic, water-logged soils, which leads to increased emissions of N20, a gas that contributes to climate change. As a result, increased macroporosity reduces denitrification in the soil, by allowing oxygen to penetrate into the topsoil, and reducing the chances of water logging.

It’s amazing to see evidence of how organic techniques allow our earthworm friends to flourish, and how positive their presence is in orchard soils!