Healthy soils for healthy cities:
Why soil health matters for urban consumers – and how biochar can help

– 05 December 2025 –

Just beyond the main gate at WorldVeg headquarters in Taiwan, a field of okra sways in the breeze alongside high-rise apartments. These tall green plants with pale yellow blooms are a stone’s throw from the center of Shanhua District, with its hundreds of eateries. It’s a fitting scene for UN World Soil Day 2025, which reminds us that urban nutrition is rooted in soil health.

Towns and cities depend on vegetables for diverse, healthy diets – through restaurants, food businesses, and home cooking – and sustainable vegetable production depends on healthy soils. Yet vegetable farmers are facing increasing challenges linked to climate change, from rising temperatures to mounting pest and disease pressure. At the same time, agriculture contributes heavily to the problem: current agri-food systems produce one-third of all global greenhouse gas emissions. 

Intensive vegetable production systems are no exception. Frequent tillage and heavy use of synthetic fertilizers degrade soil and generate significant emissions – especially nitrous oxide, a greenhouse gas 273 times more potent than CO₂. It can also upset the natural balance of soil biodiversity and break down soil organic matter, weakening the foundations of sustainable vegetable production and undermining climate resilience.

To meet these challenges, WorldVeg has been trialling vegetable production using a range of agroecological approaches  – these are recognised by the Intergovernmental Panel on Climate Change (IPCC) for their contribution to climate adaptation and mitigation. They focus on improving soil health: building organic matter, increasing biodiversity, improving water retention, and reducing reliance on synthetic fertilizers. 

And that brings us back to the okra swaying in the breeze on the edge of Shanhua town. These WorldVeg trials are using different applications of biochar – a charcoal-like material produced by heating crop residues and other organic waste in low-oxygen conditions and applied to soils to improve fertility, increase carbon storage, and enhance overall soil health. 

Crop research shows that the use of biochar can reduce nitrous oxide emissions by 39% on average, although the evidence from vegetable systems is limited.

The WorldVeg okra trials have already shown that biochar applications can significantly enhance production. An application rate of 30 tonnes per hectare – in combination with recommended rates of either mineral or organic fertilizer – improved plant growth and boosted yields by an impressive 35% and 41% respectively, compared to mineral and organic fertilizers without biochar. 

It also significantly improved nitrogen use efficiency – how well the plants use available nitrogen for growth – and reduced GHG emissions. 

In addition, biochar applications in the okra fields: 

  • reduced bulk density (lower bulk density means better aeration and less compaction, which is better for root growth and water percolation);
  • increased the proportion of small aggregates in the soil (tiny clumps that form when sand, silt, clay, organic matter, and microbial substances stick together, holding carbon, water, and nutrients);
  • Increased overall soil carbon sink;
  • reduced nitrous oxide emissions from the soil;
  • had no negative impacts on the diversity of the soil microbiome

These improvements suggest that broader biochar use could help farmers produce more vegetables with a lower carbon footprint – a crucial step for more sustainable and healthy food in cities and beyond.

 

 

(Clockwise left-to-right): Lukas Pawera checks WorldVeg okra-biochar trials in Shanhua District; Biochar ready for use; Lokeshwar Kesamreddy measures greenhouse gas emissions from the okra trials earlier in the season; Checking the trials on World Soil Day.

“It’s encouraging and exciting to see that solutions such as biochar have multiple wins for vegetable production – from improved soil health and increased productivity, to reduced greenhouse gas emissions,” said Lukas Pawera, Agronomist and Agroecologist at WorldVeg, who is leading the okra biochar trials.”

Besides biochar, WorldVeg is also testing various other agroecological and regenerative approaches to improving soil health. These include:

  • using black soldier fly to turn urban food waste into nutrient-rich frass, which can be used as fertilizer 
  • vermicomposting and use of bioslurry (byproduct from a biogas digester)
  • reducing tillage intensity for vegetables
  • testing organic and biodegradable mulch, and 
  • identifying options for soil and climate-friendly crop diversification

Pawera continued: “Building healthy soils today means investing in the resilience of tomorrow. That means more sustainable vegetable production and healthier consumers – wherever they may be.”