Applying biochar and biodegradable mulches on semiarid land can increase productivity and soil carbon sequestration when growing corn, according to work from China — but the approach doesn’t come without some complexities.
In the study at the Dryland Agricultural Research Station, scientists applied biochar, which can be made by carbonising any organic material under high temperature anaerobic conditions, but in this case used maize straw, to replicated plots at different rates. They covered the biochar treatments with a biodegradable mulch, which broke down in 120-180 days.
They grew corn over three seasons, measuring crop yield and collecting soil, soil water and gas samples for analysis for the years 2020 and 2021, while also measuring temperature.
Unpacking complex emissions picture
Their data revealed clear production advantages. The dual technique improved corn yield by 18.68–41.80%, as well as water efficiency, with the use of the film mulch having a particularly strong effect on this.
However, the team also saw that the relationship between the measures and greenhouse gas emissions was not entirely straightforward.
While the mulching can increase carbon dioxide and nitrous oxide by creating favourable conditions for microbial activity, these effects are mitigated by the application of biochar, with higher rates increasing this effect until a likely plateau. They also found that the film mulch significantly increased the fixed carbon in straw, grain and root biomass of the crop and also increased methane absorption.
It was at yield-scale, considering the large impact of inputs such as fertilisers, where the bigger picture could be seen, the scientists wrote in Journal of Integrative Agriculture. Mulching decreased the carbon footprint of production by 19.46% and 8.37% in the two years studied, while the application of biochar decreased it by 2.4-20.97%, depending on the quantity applied. Higher biochar application rates brought better results for emissions reduction and absorption with 9.0 tonnes per hectare–1 the likely ‘sweet spot’.
Future roles for mulch and biochar
The ubiquitous use of mulches has become a more high-profile sustainability issue in recent years. Plastic mulches in particular have been associated with soil contamination, while novel, biodegradable solutions increasingly seen as the way forward. Meanwhile, a growing body of research has linked the application of biochar to soils with increases in global carbon pools.
Dryland areas with soil low in organic matter, such as those found in China, can be particularly important for grain production. Efforts are needed to promote soil carbon sequestration and land performance in this agricultural terrain around the world, yet to date, there has been limited research on the subject.
“Based on these findings, we recommend incorporating maize straw biochar with film mulching in semiarid conditions to improve soil quality and promote the sustainable utilization and development of farmland,” the scientists concluded.
