[Commentary] To address climate change, grow and restore soil, not trees

COP26, the United Nations climate change conference this year, emphasised the urgency to limit global warming to well below 2 degrees Celsius, both via emission reductions and the sequestration of atmospheric CO₂, while ensuring a just transition to a low carbon economy.

These calls have resulted in a massive push toward tree planting. A closer investigation, however, of actual carbon stocks – the amount of carbon stored in a particular system – calls into question this enthusiasm, particularly in the semi-arid tropics.

The natural (native) land cover in these hot, dry places includes scrub forests and savannah grasslands. Indiscriminate planting of exotic deep-rooted tree species here, often results in decreasing streamflow, lowering groundwater tables and depriving herbivores of their fodder. In contrast, in these semi-arid regions, below-ground carbon (soils) can hold two to ten times the amount of carbon of above-ground carbon (vegetation).

But the potential of soils to store carbon, has hitherto not received as much attention as tree planting. Indeed, the earth’s soils contain about 2,500 gigatons of carbon, more than three times the amount of carbon in the atmosphere and four times the amount stored in all vegetation.

Boosting soil organic carbon is farmer friendly with biodiversity and water co-benefits

Soil organic carbon (SOC) content is important for climate change mitigation, but it is equally important for farmers and biodiversity.  Increasing soil carbon has the effect of drawing down carbon from the atmosphere, while simultaneously improving soil structure and soil health, soil fertility and crop yields, water retention and aquifer recharge. A soil must have at least 5% organic matter to be considered healthy.

In recent years, “carbon farming” has gained traction. It is the process of changing agricultural practices or land use to sequester carbon in soil and litter, as well as emission avoidance through better land management.

Countries like Australia are actively promoting it along with the sale of soil carbon credits. The Carbon Farmers of Australia, an advisory group, reports projects spanning 750,000 hectares. One Australian farming company recently announced a $500,000 sale of “soil carbon credits” to the technology company Microsoft, which has pledged to become carbon negative by 2030.

Soil carbon markets, however, have had difficulties even in advanced economies with very large farm sizes (>1000 ha) because anyone wanting to avail of the carbon credits has to use an approved methodology to demonstrate the carbon sequestered.

While Indian smallholder farmers would benefit greatly from being able to avail of carbon credits for shifting to regenerative practices and managing their land better, the question of whether, in practice, any of these funds will ever reach them remains to be seen; soil carbon credit markets are based on measurement, data and certification systems, which are expensive.

Read more: A new digital soil map for India could help use soil optimally

Limited baseline data on soil carbon, no data on soil biology and co-benefits

If we are to provide incentives to farmers to boost soil carbon, we need reliable data on the state and health of the soil carbon stock. In Switzerland, for instance, farmers perform mandatory analyses of the soil organic carbon content of topsoil of every field, at least every 10 years. The results are then stored in a centralised database, so the soil carbon stock of the country can be tracked over time.

In contrast, there is very little publicly available baseline data on soil carbon in India.

Moreover, while conventional agricultural sciences have focused primarily on the physical and chemical properties of soil (thus the focus on NPK by the fertiliser industry), there is an emerging body of work, that focuses on the living microorganisms in soils and how their interactions are critical to producing a range of ecosystem services.

The soil microbiome is closely linked to soil organic carbon and is largely key to providing the co-benefits associated with healthy soils, but the impact and pathways of the so-called “soil microbiome” on yields, irrigation water demand and pest resistance are only beginning to be understood. Much more basic and applied research remains to be done.

Need to empower smallholder farmers

By using methods of regenerative agriculture, it is possible to not only increase the amount of soil organic carbon (SOC) in existing soils, but to build new soil. While there are substantial benefits to the climate, it will be challenging to get smallholder farmers to benefit through direct payments because of the high transaction costs involved. In the Indian context, perhaps the payments for soil carbon improvements may ultimately have to be routed through government subsidies.

Ultimately, farmers still need to be empowered to understand and improve their soil quality. For this, programmes with farming communities on soil health are crucial. To begin with, farmers can be taught a simple “jar test” to measure their soil organic carbon. The farmers fill half a transparent plastic bottle with soil and the rest up with water, with a bit of air at the top.  After shaking the sample vigorously and setting aside for 24 hours, sedimentation occurs in the form of layers. The bottom-most (heaviest) layer is always sand; above that, is silt and then clay. The topmost layer, floating on the water, is the organic matter, which should cover at least a third of the surface.

A recent paper in the journal Nature called for the establishment of a “soil information system containing localised information on soil group, degradation status, crop yield gap, and the associated carbon-sequestration potentials” as an important first step. But this would need to be followed by policies that incentivise “carbon farming,” helping smallholders and building their capacity to transition to regenerative practices.

If we build our soils, our crops will grow themselves while helping the climate crisis.

Read more: Compensatory afforestation unlikely to make up for the loss of carbon stocks

Veena Srinivasan and G. Ravikanth are Senior Fellows at the Ashoka Trust for Research in Ecology and the Environment, Bengaluru. P. Srinivas (Soil) Vasu the founder of NGO, SOIL. Views are personal.

Banner image: The sprouting of maize. Photo by Roman Synkevych/Unsplash.