Grazing animals key to long-term soil carbon stability: IISc study

Subject: Environment

Context-

A study carried out by researchers at the Centre for Ecological Sciences (CES) and the Divecha Centre for Climate Change (DCCC), IISc, has revealed that grazing animals hold the key to long-term soil carbon stability.

Research finding-

The 16-year-long study carried out by CES and DCCC researchers state that large mammalian herbivores like the Yak and Ibex play a crucial role in stabilising the pool of soil carbon in grazing ecosystems such as the Spiti region in the Himalayas.
Experimental removal of grazing by herbivores from such ecosystems was found to increase the fluctuations in the level of soil carbon, which can have unintended negative consequences for the global carbon cycle, the study revealed.
Since soil contains more carbon than all plants and the atmosphere combined, it is important to ensure its persistence.
When plants and animals die, the dead organic matter remains in the soil for a long duration before microbes break it down and release carbon into the atmosphere as carbon dioxide.

Reliable sink

The soil pool is a reliable sink for trapping carbon.
Maintaining stable levels of carbon in the soil is, therefore, key to offsetting the effects of climate change.

Fluctuations in soil carbon

From one year to the next, soil carbon was found to fluctuate 30-40% more in the fenced plots where animals were absent, compared to the grazed plots where it remained more stable each year.
A key factor underlying these fluctuations was nitrogen.
Depending on the soil conditions, nitrogen can either stabilise or destabilise the carbon pool. Grazing by herbivores, however, changes their interactions in ways that tip the balance in favour of the former.
These fluctuations can be consequential for climate as they are linked to how large mammalian herbivores influence soil.
As grazing ecosystems make up about 40% of the Earth’s land surface, protecting the herbivores that keep the soil carbon stable should remain a key priority for mitigating climate change.

How effective soil as carbon sinks?

SOC –

Soil organic carbon (SOC) comes from plants, animals, microbes, leaves and wood, mostly found in the first metre or so.
Soils contain around 2,300 Gt (1 gigatonne = 1 billion tonnes) of organic carbon, making this the largest terrestrial carbon pool.

Benefits –

Increasing SOC through various methods can improve soil health.
It can contribute to agricultural yield, food security, and water quality, and also reduce the need for chemicals.
It helps address carbon mitigation and also improves conditions of fresh water, biodiversity, land use and nitrogen use.
Moreover, carbon sequestration in soils has the potential to offset GHG emissions from fossil fuels by up to 15% annually.
Utilising this option would thus offer breathing time before other technologies can help to transit to a zero-carbon lifestyle.

How is it achieved?

There are many conditions and processes that determine changes to SOC content.
These include temperature, rainfall, vegetation, soil management and land-use change.
Thus, increasing Soil Organic Carbon involves adopting sustainable agricultural practices to keep these factors in balance.
The approaches to increase SOC include:
- reducing soil erosion
- no-till-farming
- use of cover crops
- nutrient management
- applying manure and sludge
- water harvesting and conservation
- agroforestry practices, etc