Assessing the potential of urban soil for carbon sequestration by adding wheat straw pellets or wheat straw biochar

Higher Education in England targets to reduce by an average 34% carbon dioxide emissions until 2020 based on the level in 1990. This project not only requires various departments of universities to improve their energy system by utilizing low carbon techniques but also challenges the academics and researchers to examine multiple approaches to sequester carbon as much as possible in the limited area. Land owned by universities contains a lot of carbon. The group SUCCESS (Sustainable Urban Carbon Capture Engineering Soils for Climate Change) in Newcastle University has observed that 10 ha of urban soil near Newcastle Science Central removed almost 80 T CO₂ per hectare every month.

The project has set up two lysimeters in June 2018 to investigate the addition of wheat straw pellets (WP) versus biochar (BC) produced from this biomas as carbon sequestration strategies. Sensors were set up at different depths to collect information about the internal soil environment. The wheat straw biochar has 69.04% C content, and it was applied to the soil at a rate of 2% (w/w); the application rate of wheat straw pellets is based on the carbon weight of wheat straw biochar. Therefore, the amount of carbon added as wheat straw pellets, or as wheat straw biochar was 29.8±0.57 Kg in each lysimeter.

Cumulatively, 704.23±0.14 g and 697.17±0.1 g of total carbon were leached from the lysimeter BC and lysimeter WP, respectively, till the end of November 2019. Meanwhile, the total amount of CO2 carbon released via respiration of soil carbon was 9.65±0.35 Kg and 6.17±0.19 Kg for lysimeter BC and lysimeter WP, respectively, from August 2018 to November 2019. Moreover, the carbon mass fixed, measure as dried grass biomass in the two systems was 1.57 Kg for lysimeter BC and 1.75 Kg for lysimeter WP. The net C mass stored according to the mass balance for the lysimeter BC is 21.02 ±0.67 Kg from the topsoil during the experiment period, and 24.68±0.6 Kg in lysimeter WP. Whereas, by measurement, the amount of carbon in the topsoil has shown an increase of 37.09±13.58 Kg and 19.51±3.36 Kg in lysimeter BC and lysimeter WP, respectively. Currently, the data obtained in this study indicate that the mixture of biochar and biomass amendment promotes carbon sequestration potential in the urban soil environment and further application details on land owned by the university can be explored.