Carbon sequestration is rising on China’s farmland thanks to changes in agricultural practises, a large-scale piece of data analysis suggests.
Scientists at Northwest A&F University started with two data sets on net ecosystem productivity, from 2000-2020 and 2001-2021, respectively, covering metrics such as land, meteorological conditions, soil microbial respiration and carbon emissions. They then combined these with two data sets on land use, plus climate and socio-economic data, and used statistical modelling approaches to examine links between human activities and ecosystem productivity.
They found that from 2010, China’s farmland shifted from being a source of carbon emissions to a carbon sink, with over 75% of farms showing increasing carbon sequestration.
The changes were more marked in the north of the country, where wheat and corn, among the most efficient crops for carbon sequestration, are primarily produced. On over 50% farmland, ecosystem productivity had significantly increased, with the northern region contributing to nearly 70% of this.
Tillage, cropping changes make impact
The human interventions most associated with carbon sink improvements were an increase in no-tillage growing and growing of multiple crops in fields over the course of a year, as well as land consolidation.
No till reduces soil disturbance, resulting in higher soil moisture and lower temperature than conventional tillage, which slows carbon turnover, they noted in the journal Nature Communications.
Another factor in the sequestration increase is the incorporation of straw from grain production back into the soil, providing a direct carbon source. This approach is actively recommended by the Chinese government in grain-producing areas, and whilst the team warned that excessive use of this technique can result in acidification of soils and the introduction of diseases, when used judiciously it “yields greater benefits than drawbacks,” they wrote.
The researchers also found considerable interaction between the various measures instigated on farms.
“In general, the continuous development and advancement of conservation tillage, such as no till and mechanised straw returning, play a crucial role in soil and water conservation, reducing greenhouse gas emissions, and providing a significant opportunity for China’s farmland to sequester atmospheric carbon,” they said.
Careful decisions needed to continue progress
Not all human interventions meant greater soil carbon, however. They scientists that low rates of straw return and excessive irrigation suppressed the carbon sequestration potential of farmland, recommending a shift towards drip irrigation and the application of moderate amounts of straw to fields.
“Our results show that it is imperative to acknowledge the crucial role of human interventions on farmland net ecosystem productivity, to strike a balance between food security and farmland carbon sequestration,” they added.